Merge pull request #1813 from rspec/a-few-small-changes

A few small changes
Keep benchmark working.
Apply module inclusion to individual examples when filtered.

Previously it only applied to filtered groups. Luckily,
ruby’s object model supports this very easily through
the use of singleton classes.
Ensure shared contexts applied to one example have their hooks run.
Got things to work on 1.8.7.
Run `:context` hooks from shared contexts that apply to one example.
Make :context hooks in config apply to individual matching examples.
Skip specs failing due to a JRuby 1.7 bug when run in ruby 2.0 mode.
Add benchmarks for treating an example’s group instance’s singleton class as a group.