ThugLogging `log_warning' method

	The new ThugLogging method `log_warning' is meant to be used in order to
	notify runtime warnings and errors in real time (currently just through
	the HPFeeds infrastructure).
Avoid potential crashes due to errors in Javascript execution

	This patch allows to continue the analysis (if possible) avoiding potential
	crashes due to errors in Javascript execution. Moreover every run-time error
	and warning is notified through the ThugLogging `log_warning' method.