Merge branch 'maint'

* maint:
  difftool: provide basename to external tools
  git-difftool.txt: correct the description of $BASE and describe $MERGED

Documentation/git-difftool.txt

@@ -56,14 +56,16 @@ the configured command line will be invoked with the following
 variables available: `$LOCAL` is set to the name of the temporary
 file containing the contents of the diff pre-image and `$REMOTE`
 is set to the name of the temporary file containing the contents
-of the diff post-image.  `$BASE` is provided for compatibility
-with custom merge tool commands and has the same value as `$LOCAL`.
+of the diff post-image.  `$MERGED` is the name of the file which is
+being compared. `$BASE` is provided for compatibility
+with custom merge tool commands and has the same value as `$MERGED`.
 
 -x <command>::
 --extcmd=<command>::
 	Specify a custom command for viewing diffs.
 	'git-difftool' ignores the configured defaults and runs
 	`$command $LOCAL $REMOTE` when this option is specified.
+	Additionally, `$BASE` is set in the environment.
 
 -g::
 --gui::

git-difftool--helper.sh

@@ -49,6 +49,7 @@ launch_merge_tool () {
 	fi
 
 	if use_ext_cmd; then
+		export BASE
 		eval $GIT_DIFFTOOL_EXTCMD '"$LOCAL"' '"$REMOTE"'
 	else
 		run_merge_tool "$merge_tool"