CancelableWait in misc.c should check for negative timeout

[Tor Lillqvist]

Tor Lillqvist writes:
 >   if (((int) timeout) < 0)
 >     timeout = 0;

Actually, as INFINITE is 0xFFFFFFFF, i.e. -1, this code snippet
shouldn't be in CancelableWait, but in pthreadCancelableTimedWait.

--tml