All tests passing on MRI 2.0

Added support for Binding#frame_type, via frame_iseq in RubyVM::DebugInspector.
Note it just appeared like the 10th element in iseq.to_a returns the frame type
but this could potentially be unreliable, though it seems to work fine. :D
ArgumentError -> RuntimeError
version 0.6.9pre1 release

* added support for Binding#frame_type, improved binding collection.
* pry-stack_explorer now passes its test suite using this gem