bash-completion: Add non-command git help files to bash-completion

Git allows access to the gitattributes man page via `git help attributes`,
but this is not discoverable via the bash-completion mechanism.  This
patch adds all current non-command man pages to the completion candidate
list.

Signed-off-by: Marcus Griep <marcus@griep.us>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -885,7 +885,11 @@ _git_help ()
 		return
 		;;
 	esac
-	__gitcomp "$(__git_all_commands)"
+	__gitcomp "$(__git_all_commands)
+		attributes cli core-tutorial cvs-migration
+		diffcore gitk glossary hooks ignore modules
+		repository-layout tutorial tutorial-2
+		"
 }
 
 _git_init ()