Merge pull request #177 from kellypleahy/topic/fix-delete-mutex

Fix bug in the way pthead_mutex_t was being destroyed in win32.

src/win32/pthread.c

@@ -55,9 +55,8 @@ int pthread_mutex_init(pthread_mutex_t *GIT_RESTRICT mutex,
 
 int pthread_mutex_destroy(pthread_mutex_t *mutex)
 {
-    int ret;
-    ret = CloseHandle(mutex);
-    return -(!ret);
+    DeleteCriticalSection(mutex);
+    return 0;
 }
 
 int pthread_mutex_lock(pthread_mutex_t *mutex)