Merge branch 'jc/t1512-fix'

A test that should have failed but didn't revealed a bug that needs
to be corrected.

* jc/t1512-fix:
  get_short_sha1(): correctly disambiguate type-limited abbreviation
  t1512: correct leftover constants from earlier edition

diff --cc sha1_name.c
Simple merge

diff --cc t/t1512-rev-parse-disambiguation.sh
Simple merge