Integrate semaphores extension from Craig McPeeters' branch on

public.perforce.com (revisions 1664, 1665).


[SVN r16472]

tools/build

@@ -1 +1 @@
-Subproject commit a8d2feea847d9dbd53220647d0886739dd3ce245
+Subproject commit 0cd123a2db9f3d32297140272dedc2ba8c8c4e94