Warn arity mismatch on shared examples

* helps when users migrate from rspec-1 to rspec-2
* see issue #1066
clean up warning for more than one arg to include_examples

* support warning for Ruby >= 1.9
* use CallerFilter
* improve wording of warning
improve precision of warning for unexpected args to include_examples and its aliases
Merge pull request #1067 from rspec/issue-1066

warn when the name of more than one example group is submitted to `include_examples` and it's aliases