#1510 Test RKObjectResponseMapperOperation's HTTP method-based matching

The test checks to make sure RKObjectResponseMapperOperation filters the
provided response descriptors based on the HTTP method (and not just by
URL and status code).

Test fails against commit 18087af9cbf1f0743aaf3e6955dfd9ddb1a4aec5
Test passes starting with 49209e0e36a366e0d1521331579f9f8c68ea7daa