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.
I'm running into an issue where the `ExampleGroup` instance that represents a `before(:context)` is the same object for each `before(:context)`. Since that's the case, I'm not able to specify a line number specific inspect output. Right now, I am using the first `hook_description` to populate the `before(:context)` `ExampleGroup#inspect`:

    hooks[:before][:context].first.hook_description

I wanted to check with you before committing anything in case I am missing something.