x/debug: Add types for representing Func and Interface values, and add an address field to Channel.

Func just contains an address for the function struct, and Interface holds no
information for now.

Fixes some comments in program.go.

For Channels, store the address of the channel struct as well as the
address of the queue buffer.

Change-Id: I5b103f0d3b049270c3a04a700f52ec3afdb47734
Reviewed-on: https://go-review.googlesource.com/15521
Reviewed-by: Dave Day <djd@golang.org>
5 files changed