Documentation: turn middle-of-line tabs into spaces

These tabs happen to appear in columns where they don't stand out too
much, so the diff here is non-obvious. Some of these are rendered
differently by AsciiDoc and Asciidoctor (although the difference might
be invisible!), which is how I found a few of them. The remainder were
found using `git grep "[a-zA-Z.,)]$TAB[a-zA-Z]"`.

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

Documentation/git-http-backend.txt

@@ -162,7 +162,7 @@ ScriptAliasMatch ^/git/[^/]*(.*) /usr/libexec/git-core/git-http-backend/storage.
 
 Accelerated static Apache 2.x::
 	Similar to the above, but Apache can be used to return static
-	files that are stored on disk.	On many systems this may
+	files that are stored on disk.  On many systems this may
 	be more efficient as Apache can ask the kernel to copy the
 	file contents from the file system directly to the network:
 +