GLOBAL MARKETS-Shares hit six-month low as growth worries mount

* MSCI All-Country World index hits six-month low* Benchmark on track for third straight weekly loss* Brent crude at lowest level since Dec 2010* Investors fret about global slowdown as Fed stimulus endsBy Francesco CanepaLONDON, Oct 10 (Reuters) - Global shares fell to a six-month trough and Brent crude futures tumbled to their lowest since 2010 on Friday as investors worried about the prospect o