I'm having problems opening a pull request for this for some reason. This fixes the spec failures on 1.9.2 that you mentioned earlier today. It was caused by RSpec::Matchers being included multiple times causing its method_missing hook to infinitely super to itself.
Justin's recent contribution to allow other expectations/assertion libraries triggered this. I wasn't sure if you wanted to remove the include from here or there (is it better for rspec-core to take care of including matchers, or matchers to take care of including itself in core?).
Anyhow this fixes the problem, and includes a spec to test that the method_missing supering works properly.
Fix infinite recursion SystemStackError on 1.9.2.
RSpec::Matchers#method_missing calls super, and it was supering to itself infinitely because RSpec::Matchers was being included multiple times. rspec-core now takes care of including RSpec::Matchers on its as of this commit: