Assimilate exceptions and RefPtr from mspmisc

Assimilate GetOpt
Do not require pthread on win32
Add an optional feature to generate backtraces on exceptions
Allow semaphores to be created with an external mutex
Rewrite win32 semaphore implementation to more closely correspond the POSIX one
Allow MutexLock to be unlocked initially
Rewrite MutexPtr to use a RefPtr<MutexLock> instead of being refcounted itself
Fix some multiple inclusion guards
Add $Id$ tags
Fix Time::now() on win32