Uninline prefixcmp()

Uninline prefixcmp()

Now the routine is an open-coded loop that avoids an extra
strlen() in the previous implementation, it got a bit too big to
be inlined.  Uninlining it makes code footprint smaller but the
result still retains the avoidance of strlen() cost.

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