Added a thread-safe and robust wrapper for APR pools.

See http://redmine.imprudenceviewer.org/issues/590
and https://jira.secondlife.com/browse/SNOW-596

indra/llcommon/llerror.cpp

@@ -877,6 +877,9 @@ You get:
 	
 */
 
+apr_thread_mutex_t* gLogMutexp;
+apr_thread_mutex_t* gCallStacksLogMutexp;
+
 namespace {
 	bool checkLevelMap(const LevelMap& map, const std::string& key,
 						LLError::ELevel& level)