Merge branch 'jc/retire-get-sha1-hex'

The implementation of "get_sha1_hex()" that reads a hexadecimal
string that spells a full object name has been extended to cope
with any hash function used in the repository, but the "sha1" in
its name survived.  Rename it to get_hash_hex(), a name that is
more consistent within its friends like get_hash_hex_algop().

* jc/retire-get-sha1-hex:
  hex: retire get_sha1_hex()

diff --cc packfile.c
Simple merge

diff --cc rerere.c
Simple merge