- Unset the proper bit in the bitmap that keeps track which structures
are in use and which aren't when the thread exits.
- Protect the bitmap using PROC_SLOCK.

Discussed with:	attilio[1]
Pointed out by:	jhb[2]
Add hooks for process_exit/process_exec so taht schedctl structures
are deallocated (avoiding a leakage). This rely on EVENTHANDLER so we
need to push forward the time when schedctl_init() is called during
boot process.
Remove redundant function prototypes (they're already in the header).
While here remove a debugging knob left accidentally there (oops).