Merge branch 'bc/hash-independent-tests'

Various tests have been updated to make it easier to swap the
hash function used for object identification.

* bc/hash-independent-tests:
t5318: use test_oid for HASH_LEN
t1407: make hash size independent
t1406: make hash-size independent
t1405: make hash size independent
t1400: switch hard-coded object ID to variable
t1006: make hash size independent
t0064: make hash size independent
t0002: abstract away SHA-1 specific constants
t0000: update tests for SHA-256
t0000: use hash translation table
t: add test functions to translate hash-related values

diff --cc t/README
Simple merge

diff --cc t/t1400-update-ref.sh
Simple merge

diff --cc t/test-lib-functions.sh
Simple merge