Prepare synchronization with viewer-development.

Synchronization will be complete after viewer-development
gets my LLAPRPool and LLAPRFile patch that I'm currently
working on.

indra/llcommon/llthread.cpp

@@ -399,6 +399,15 @@ LLMutexBase::LLMutexBase() :
 {
 }
 
+bool LLMutexBase::isSelfLocked() const
+{
+#if LL_DARWIN
+	return mLockingThread == LLThread::currentID();
+#else
+	return mLockingThread == local_thread_ID;
+#endif
+}
+
 void LLMutexBase::lock() 
 { 
 #if LL_DARWIN
@@ -431,7 +440,7 @@ void LLMutexBase::unlock()
 
 	apr_thread_mutex_unlock(mAPRMutexp);
 }
-	
+
 //----------------------------------------------------------------------------
 
 //static