Ensure backtraces start at user code, not rspec-mocks code

[onlynone]

This will ensure all exceptions generated by rspec-mocks have the first line of their backtraces pointing to the user's code where the error happened.

Addresses #1592

[pirj]

HunkGenerator on 2.2 and 2.5 is flaky.

[pirj]

Do you need some help with JRuby support?

[JonRowe]

We already handle this in rspec-core and as per #1592 I don't want to add the maintenance burden of this, it would duplicate logic we have elsewhere. Additionally to our filtering we also have the ability to remove the filtering to allow finding issues within our, or any other filtered out code which this would circumvent.