Merge branch 'bw/short-ref-strict'

* bw/short-ref-strict:
remote.c: use shorten_unambiguous_ref
rev-parse: --abbrev-ref option to shorten ref name
for-each-ref: utilize core.warnAmbiguousRefs for :short-format
shorten_unambiguous_ref(): add strict mode

diff --cc remote.c
Simple merge