resolve_ref(): turn buffer into a proper string as soon as possible
Immediately strip off trailing spaces and null-terminate the string
holding the contents of the reference file; this allows the use of
string functions and avoids the need to keep separate track of the
string's length. (get_sha1_hex() fails automatically if the string is
too short.)
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>