[win32] Various win32 fixes

[win32] Various win32 fixes
 - support spawn via system(&P_NOWAIT,...) like OS2
 - support wait() and waitpid()
 - s/GetCurrentDirectory/GetCwd/, long-named XS to be removed
 - support -lfoo properly in ExtUtils::Liblist
 - fix outdated info about Win32 support in perlfaq2
 - fix win32 bug in perldoc that causes spurious warnings
 - regularize global function/variable names yet more
 - fix bug in do_aspawn() (it was always invoking shell, instead of
   almost never)
 - implement and export win32_wait()
 - stub version of USE_RTL_THREAD_API

p4raw-id: //depot/win32/perl@391