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/newview/llviewerprecompiledheaders.h

@@ -164,7 +164,7 @@
 #include "llinstantmessage.h"
 #include "llinvite.h"
 //#include "llloginflags.h"
-#include "llmail.h"
+//#include "llmail.h"
 #include "llmessagethrottle.h"
 #include "llnamevalue.h"
 #include "llpacketack.h"