31b808a0

 (clone --single: limit the fetch refspec to fetched branch,
2012-09-20) tried to see if the given "branch" to follow is actually
a tag at the remote repository by checking with "refs/tags/" but it
incorrectly used strstr(3); it is actively wrong to treat a "branch"
"refs/heads/refs/tags/foo" and use the logic for the "refs/tags/"
ref hierarchy.  What the code really wanted to do is to see if it
starts with "refs/tags/".

Signed-off-by: Junio C Hamano <gitster@pobox.com>