Added Pry.last_internal_error

Holds the last internal error (such as CommandError, Slop::InvalidOptionError,
or MethodSource::SourceNotFoundError). Useful for debugging commands.
Just set: _pry_.last_exception = Pry.last_internal_error
version 0.9.11.4 release

* fixed pager bug (wouldn't render color codes in some circumstances)
* added Pry.last_internal_error, useful for devs debugging commands