Westport Innovations (WPRT) inked another natural gas motor deal with General Motors (GM) on Wednesday, Westport's latest pact with big vehicle and engine makers amid decade-low U.S. natgas prices. Shares of the engine maker rose 9.7% to 35.66 at midday. GM shares edged up 0.2% from Tuesday's 2012 low. The second deal with GM will allow Westport to develop natural gas engine technology for light-duty vehicles such as sedans, pickup trucks and