GLOBAL MARKETS-Gaza violence, plane crash in Ukraine hit stocks

* Crash of Malaysian airliner sparks risk-aversion * Russian assets fall on U.S., EU sanctions * U.S. housing starts weak; Morgan Stanley results up (Recasts top two paragraphs, changes headline, changes quote) By Ryan Vlastelica NEW YORK, July 17 (Reuters) - Global stock markets slumped on Thursday, while safe-haven gold and bond prices rose following an escalation of violence in Gaza and the downing of a passenger plane at the Ukraine-Russia border. Wall Street had its wo