libc: add sanity checks to pthread_mutex_destroy()

Change-Id: Iddb2204fa792fa9aca5f19838926dddbb09b74a2
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index 83703d8..5a7a1ac 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -3,7 +3,9 @@
 
 Differences between current and Android 2.2:
 
-- <pthread.h>: Add reader/writer locks implementation.
+- <pthread.h>: Add reader/writer locks implementation. Add sanity
+  checking to pthread_mutex_destroy() (e.g. a locked mutex will return
+  EBUSY).
 
 - <semaphore.h>: Use private futexes for semaphore implementation,
   unless your set 'pshared' to non-0 when calling sem_init().