Work around em-dash handling in newer AsciiDoc

Older versions of AsciiDoc used to literally pass double dashes when we
used them in our linkgit macros and manpage titles, but newer ones (the
issue was first reported with AsciiDoc 8.5.2) turn them into em dashes.

Define litdd (literal double-dash) custom attribute in asciidoc.conf to
work this around.  While we are at it, fix a few double-dashes (e.g. the
description of "project--devo--version" convention used by tla, among
other things) that used to be incorrectly written as em dashes in the body
text to also use this attribute.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/asciidoc.conf

@@ -18,6 +18,7 @@ startsb=[
 endsb=]
 tilde=~
 backtick=`
+litdd=--
 
 ifdef::backend-docbook[]
 [linkgit-inlinemacro]

Documentation/git-add.txt

@@ -220,7 +220,7 @@ binary so line count cannot be shown) and there is no
 difference between indexed copy and the working tree
 version (if the working tree version were also different,
 'binary' would have been shown in place of 'nothing').  The
-other file, git-add--interactive.perl, has 403 lines added
+other file, git-add{litdd}interactive.perl, has 403 lines added
 and 35 lines deleted if you commit what is in the index, but
 working tree file has further modifications (one addition and
 one deletion).

Documentation/git-archimport.txt

@@ -44,7 +44,7 @@ archives that it imports, it is also possible to specify git branch names
 manually.  To do so, write a git branch name after each <archive/branch>
 parameter, separated by a colon.  This way, you can shorten the Arch
 branch names and convert Arch jargon to git jargon, for example mapping a
-"PROJECT--devo--VERSION" branch to "master".
+"PROJECT{litdd}devo{litdd}VERSION" branch to "master".
 
 Associating multiple Arch branches to one git branch is possible; the
 result will make the most sense only if no commits are made to the first
@@ -85,8 +85,8 @@ OPTIONS
 -o::
 	Use this for compatibility with old-style branch names used by
 	earlier versions of 'git archimport'.  Old-style branch names
-	were category--branch, whereas new-style branch names are
-	archive,category--branch--version.  In both cases, names given
+	were category{litdd}branch, whereas new-style branch names are
+	archive,category{litdd}branch{litdd}version.  In both cases, names given
 	on the command-line will override the automatically-generated
 	ones.
 

Documentation/git-help.txt

@@ -55,9 +55,9 @@ other display programs (see below).
 +
 The web browser can be specified using the configuration variable
 'help.browser', or 'web.browser' if the former is not set. If none of
-these config variables is set, the 'git web--browse' helper script
+these config variables is set, the 'git web{litdd}browse' helper script
 (called by 'git help') will pick a suitable default. See
-linkgit:git-web--browse[1] for more information about this.
+linkgit:git-web{litdd}browse[1] for more information about this.
 
 CONFIGURATION VARIABLES
 -----------------------
@@ -80,7 +80,7 @@ help.browser, web.browser and browser.<tool>.path
 The 'help.browser', 'web.browser' and 'browser.<tool>.path' will also
 be checked if the 'web' format is chosen (either by command line
 option or configuration variable). See '-w|--web' in the OPTIONS
-section above and linkgit:git-web--browse[1].
+section above and linkgit:git-web{litdd}browse[1].
 
 man.viewer
 ~~~~~~~~~~

Documentation/git-instaweb.txt

@@ -44,9 +44,9 @@ OPTIONS
 -b::
 --browser::
 	The web browser that should be used to view the gitweb
-	page. This will be passed to the 'git web--browse' helper
+	page. This will be passed to the 'git web{litdd}browse' helper
 	script along with the URL of the gitweb instance. See
-	linkgit:git-web--browse[1] for more information about this. If
+	linkgit:git-web{litdd}browse[1] for more information about this. If
 	the script fails, the URL will be printed to stdout.
 
 --start::
@@ -79,7 +79,7 @@ You may specify configuration in your .git/config
 
 If the configuration variable 'instaweb.browser' is not set,
 'web.browser' will be used instead if it is defined. See
-linkgit:git-web--browse[1] for more information about this.
+linkgit:git-web{litdd}browse[1] for more information about this.
 
 Author
 ------

Documentation/git-mergetool--lib.txt

@@ -1,5 +1,5 @@
-git-mergetool--lib(1)
-=====================
+git-mergetool{litdd}lib(1)
+==========================
 
 NAME
 ----
@@ -16,11 +16,11 @@ This is not a command the end user would want to run.  Ever.
 This documentation is meant for people who are studying the
 Porcelain-ish scripts and/or are writing new ones.
 
-The 'git-mergetool--lib' scriptlet is designed to be sourced (using
+The 'git-mergetool{litdd}lib' scriptlet is designed to be sourced (using
 `.`) by other shell scripts to set up functions for working
 with git merge tools.
 
-Before sourcing 'git-mergetool--lib', your script must set `TOOL_MODE`
+Before sourcing 'git-mergetool{litdd}lib', your script must set `TOOL_MODE`
 to define the operation mode for the functions listed below.
 'diff' and 'merge' are valid values.
 

Documentation/git-web--browse.txt

@@ -1,5 +1,5 @@
-git-web--browse(1)
-==================
+git-web{litdd}browse(1)
+=======================
 
 NAME
 ----
@@ -7,7 +7,7 @@ git-web--browse - git helper script to launch a web browser
 
 SYNOPSIS
 --------
-'git web--browse' [OPTIONS] URL/FILE ...
+'git web{litdd}browse' [OPTIONS] URL/FILE ...
 
 DESCRIPTION
 -----------
@@ -71,7 +71,7 @@ browser.<tool>.cmd
 When the browser, specified by options or configuration variables, is
 not among the supported ones, then the corresponding
 'browser.<tool>.cmd' configuration variable will be looked up. If this
-variable exists then 'git web--browse' will treat the specified tool
+variable exists then 'git web{litdd}browse' will treat the specified tool
 as a custom command and will use a shell eval to run the command with
 the URLs passed as arguments.