git-merge-base.txt: render indentations correctly under Asciidoctor

There are several graphs in this document. For most of them, we use a
single leading tab to indent the whole graph, and then we use spaces
(possibly eight or more) to align things within the graph.

In the larger graph, we use a different strategy: We use 1-N tabs and
just a small number of spaces (<8). This is how we usually prefer to do
our indenting, but Asciidoctor ends up rendering this differently from
AsciiDoc. Same thing for the if-then-fi examples where the conditional
code is indented by two tabs, which renders differently under AsciiDoc
and Asciidoctor.

Similar to 379805051d ("Documentation: render revisions correctly under
Asciidoctor", 2018-05-06), use an explicit literal block to indicate
that we want to keep the leading whitespace in the tables. Change not
just the ones that render differently, but all of them for consistency.

Because this gives us some extra indentation, we can remove the one that
we have been carrying explicitly. That is, drop the first tab of
indentation on each line. With AsciiDoc, this results in identical
rendering before and after this commit, both for git-merge-base.1 and
git-merge-base.html.

A less intrusive change would be to replace tabs 2-N on each line with
eight spaces. But let's follow the example set by 379805051d, so that we
can use our preferred way of indenting.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-merge-base.txt

@@ -80,9 +80,11 @@ which is reachable from both 'A' and 'B' through the parent relationship.
 
 For example, with this topology:
 
-	         o---o---o---B
-	        /
-	---o---1---o---o---o---A
+....
+	 o---o---o---B
+	/
+---o---1---o---o---o---A
+....
 
 the merge base between 'A' and 'B' is '1'.
 
@@ -90,21 +92,25 @@ Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the
 merge base between 'A' and a hypothetical commit 'M', which is a merge
 between 'B' and 'C'.  For example, with this topology:
 
-	       o---o---o---o---C
-	      /
-	     /   o---o---o---B
-	    /   /
-	---2---1---o---o---o---A
+....
+       o---o---o---o---C
+      /
+     /   o---o---o---B
+    /   /
+---2---1---o---o---o---A
+....
 
 the result of `git merge-base A B C` is '1'.  This is because the
 equivalent topology with a merge commit 'M' between 'B' and 'C' is:
 
 
-	       o---o---o---o---o
-	      /                 \
-	     /   o---o---o---o---M
-	    /   /
-	---2---1---o---o---o---A
+....
+       o---o---o---o---o
+      /                 \
+     /   o---o---o---o---M
+    /   /
+---2---1---o---o---o---A
+....
 
 and the result of `git merge-base A M` is '1'.  Commit '2' is also a
 common ancestor between 'A' and 'M', but '1' is a better common ancestor,
@@ -116,11 +122,13 @@ the best common ancestor of all commits.
 When the history involves criss-cross merges, there can be more than one
 'best' common ancestor for two commits.  For example, with this topology:
 
-	---1---o---A
-	    \ /
-	     X
-	    / \
-	---2---o---o---B
+....
+---1---o---A
+    \ /
+     X
+    / \
+---2---o---o---B
+....
 
 both '1' and '2' are merge-bases of A and B.  Neither one is better than
 the other (both are 'best' merge bases).  When the `--all` option is not given,
@@ -131,18 +139,22 @@ and B is (or at least used to be) to compute the merge base between
 A and B, and check if it is the same as A, in which case, A is an
 ancestor of B.  You will see this idiom used often in older scripts.
 
-	A=$(git rev-parse --verify A)
-	if test "$A" = "$(git merge-base A B)"
-	then
-		... A is an ancestor of B ...
-	fi
+....
+A=$(git rev-parse --verify A)
+if test "$A" = "$(git merge-base A B)"
+then
+	... A is an ancestor of B ...
+fi
+....
 
 In modern git, you can say this in a more direct way:
 
-	if git merge-base --is-ancestor A B
-	then
-		... A is an ancestor of B ...
-	fi
+....
+if git merge-base --is-ancestor A B
+then
+	... A is an ancestor of B ...
+fi
+....
 
 instead.
 
@@ -154,13 +166,15 @@ topic origin/master`, the history of remote-tracking branch
 `origin/master` may have been rewound and rebuilt, leading to a
 history of this shape:
 
-	                 o---B2
-	                /
-	---o---o---B1--o---o---o---B (origin/master)
-	        \
-	         B0
-	          \
-	           D0---D1---D (topic)
+....
+		 o---B2
+		/
+---o---o---B1--o---o---o---B (origin/master)
+	\
+	 B0
+	  \
+	   D0---D1---D (topic)
+....
 
 where `origin/master` used to point at commits B0, B1, B2 and now it
 points at B, and your `topic` branch was started on top of it back
@@ -193,13 +207,15 @@ will find B0, and
 will replay D0, D1 and D on top of B to create a new history of this
 shape:
 
-			 o---B2
-			/
-	---o---o---B1--o---o---o---B (origin/master)
-		\                   \
-		 B0                  D0'--D1'--D' (topic - updated)
-		  \
-		   D0---D1---D (topic - old)
+....
+		 o---B2
+		/
+---o---o---B1--o---o---o---B (origin/master)
+	\                   \
+	 B0                  D0'--D1'--D' (topic - updated)
+	  \
+	   D0---D1---D (topic - old)
+....
 
 A caveat is that older reflog entries in your repository may be
 expired by `git gc`.  If B0 no longer appears in the reflog of the