Code cleanup.
* jk/oid-array-cleanups:
oidset: stop referring to sha1-array
ref-filter: stop referring to "sha1 array"
bisect: stop referring to sha1_array
test-tool: rename sha1-array to oid-array
oid_array: rename source file from sha1-array
oid_array: use size_t for iteration
oid_array: use size_t for count and allocation