checkout: check_linked_checkout: simplify symref parsing
check_linked_checkout() only understands symref-style HEAD (i.e. "ref:
refs/heads/master"), however, HEAD may also be a an actual symbolic link
(on platforms which support it), thus it will need to check that style
HEAD, as well (via readlink()). As a preparatory step, simplify parsing
of symref-style HEAD so the actual branch check can be re-used easily
for symbolic links (in an upcoming patch).
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>