Gr.hier_block2 implementation

If anyone is experimenting with writing their own new style hierarchical
blocks based on the undocumented code in the trunk, please contact me
off list. I am about to make a major change in the API that will break
that code.

I will convert all the existing Python blocks that have been
accumulating in the trunk (mostly stuff Tom R. and I have been
writing to test things), so this will only impact those brave souls who
have been actually using this stuff on their own.

The new style hierarchical blocks and flowgraph are a 3.1 feature under
development and not part of the release 3.0.x code base.

Johnathan C.
Corgan Enterprises LLC