show-ref: accept HEAD with --verify
Previously, when --verify was specified, show-ref would use a separate
code path which did not handle HEAD and treated it as an invalid
ref. Thus, "git show-ref --verify HEAD" (where "--verify" is used
because the user is not interested in seeing refs/remotes/origin/HEAD)
did not work as expected.
Instead of insisting that the input begins with "refs/", allow "HEAD"
as well in the codepath that handles "--verify", so that all valid
full refnames including HEAD are passed to the same output machinery.
Signed-off-by: Vladimir Panteleev <git@thecybershadow.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>