Some more work on cleanup.

Some more work on cleanup.

Original commit message from CVS:
Some more work on cleanup.
- added two functions in the scheduler _setup and _reset to initialize
the context. In the case of the cothread context we have to map the
cothread stack space onto the threads stack.
- setup/reset the scheduler context in the threads context.
- fix the ghostpad cleanup.
- slightly changed the scheduler code to cleanly remove connections.