Add better `inspect` output for ExampleGroup

Pull Request for #1590 

The only problem I ran into was that the syntax error in the after hook test produces error output while running the spec (the test still passes).

> An error occurred in an `after(:context)` hook.
>   NoMethodError: undefined method `expcts' for #<RSpec::ExampleGroups::SomeClass_3 after(:context) hook>

This is definitely not ideal because it could distract from problems with "real" after hooks. The only two options I could up with were: 1) remove the test, or 2) add a way to suppress that error. I'm interested in your thoughts on the best way to handle this.
Actually, I will still need an if statement since I am interpolating the `inspect_output` variable inside `<SomeClass inspect output goes here>`. It would look like this:

    if inspect_output
      "#<#{self.class} #{inspect_output}>"
    else
      self.inspect
    end

Since I will still need an if, I think it is better to keep it in `inspect` so I can call `super`. What are your thoughts?