* spinlock.h: New file.

* spinlock.h: New file.
(spinlock): New class.
* shared.cc: Include spinlock.h.
(memory_init): Use new spinlock methods rather than roll-your-own.  Time out
after ten seconds if shared_mem_inited is not initialized.
* sync.h: Update copyright.  Remove vanity attribution.
* sigproc.cc (sigproc_terminate): Avoid attempts to kill the signal thread
while we're still initializing or suffer a deadlock.