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/llplugin/slplugin/slplugin.cpp

@@ -183,8 +183,6 @@ int APIENTRY WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdL
 int main(int argc, char **argv)
 #endif
 {
-	ll_init_apr();
-
 	// Set up llerror logging
 	{
 		LLError::initForApplication(".");
@@ -400,8 +398,6 @@ int main(int argc, char **argv)
 
 	delete plugin;
 
-	ll_cleanup_apr();
-
 	return 0;
 }