WIP: add riak_cs_manifest_resolution:resolve_prop_bclass/2
Fix riak_cs_get_fsm:chunk() API to hide tuple use, fix content range bug

One of the Ceph tests in client_tests/python was showing a bug
with content range.

    ( cd ceph_tests/s3-tests ; env S3TEST_CONF=s3test.conf env/bin/nosetests s3tests.functional.test_s3:test_ranged_request_response_code )

The bug boiled down to a pattern matching error, 2-tuple vs 3-tuple,
the NextBlock without or with the new BClass type, respectively.  I
took the opportunity to change chunk/3 -> chunk/5 and hide the
3-tuple implementation of the NextBlock tuple.

I also got rid of some 2-tuple wrappers around the later arguments
of trim_block_value().

All EUnit tests are now passing, and all client_tests tests are
passing, yay.