Use private futexes for semaphores, unless they are initialized with pshared != 0.

Change-Id: I534e36a7171cd37037ae03b910ba71ea6968286d
Note: previously, sem_init() would return an error if pshared != 0.
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index a66e737..ce43f1e 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -5,6 +5,9 @@
 
 - <pthread.h>: Add reader/writer locks implementation.
 
+- <semaphore.h>: Use private futexes for semaphore implementation,
+  unless your set 'pshared' to non-0 when calling sem_init().
+
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 Differences between Android 2.2. and Android 2.1: