Merge branch 'dk/skip-prefix-scan-only-once'

Update implementation of skip_prefix() to scan only once; given
that most "prefix" arguments to the inline function are constant
strings whose strlen() can be determined at the compile time, this
might actually make things worse with a compiler with sufficient
intelligence.

* dk/skip-prefix-scan-only-once:
skip_prefix(): scan prefix only once

diff --cc git-compat-util.h
Simple merge