Use settings.REQUIRE_DATAFILE_CHECKSUMS to allow ingests without checksums.
Clean up previous commit.
Remove redundant settings import.
Support overriding REQUIRE_DATAFILE_CHECKSUMS=False with allowEmptyChecksums=False
Fix syntax error.
Add unit test to support change to Replica.verify
Merge pull request #273 from stevage/really_ignore_checksums

Use settings.REQUIRE_DATAFILE_CHECKSUMS to allow ingests without checksu...