Merge branch 'jc/merge-base' (early part)

This contains an evil merge to fast-import, in order to
resolve in_merge_bases() update.

git.c

@@ -256,6 +256,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		{ "ls-tree", cmd_ls_tree, RUN_SETUP },
 		{ "mailinfo", cmd_mailinfo },
 		{ "mailsplit", cmd_mailsplit },
+		{ "merge-base", cmd_merge_base, RUN_SETUP },
 		{ "merge-file", cmd_merge_file },
 		{ "mv", cmd_mv, RUN_SETUP | NOT_BARE },
 		{ "name-rev", cmd_name_rev, RUN_SETUP },