As suggested by carlosmn, git_oid_ncmp would probably
be a better name than git_oid_match, for it does the same
as git_oid_cmp but only up to a certain amount of hex digits.
Set of methods to find the minimal-length to uniquely identify every OID
in a list. Useful for GUI applications, commit logs and so on.
Includes stress test.
Signed-off-by: Vicent Marti <tanoku@gmail.com>