Disable monkey patching.

Most of this conversion was done with transpec, but I had to
discard some of its changes by hand since we test some
deprecated/disallowed things here.
Merge two example groups.

No need to have two example groups for PositiveExpectationHandler.
Merge pull request #579 from rspec/disable-monkey-patching

Disable monkey patching
Fix arity check for yield matchers.
Fix warnings produced by output matcher.
Support compound block expectations.

For #552.