a lock and condvar according to the nspr documentation. r=valeski
Also I fix a problem where we would wake up from a wait without checking
any data which could cause all sorts of problems.
b=50634
mozilla/nsprpub/lib/ds/plevent.h, revision 3.12) and plevent.c
(same as mozilla/nsprpub/lib/ds/plevent.c, revision 3.36) to
mozilla/xpcom/threads. These two new files have not been added
to the makefiles or project file, so they are not picked up by
the build.