Used JSCS and fixed violations

Part of the task of bringing JSCS to grunt core: https://github.com/gruntjs/grunt/issues/1247
I've seen this style quite a bit thus far. It's a violation of disallowing multiple variable declarations, but is only used for undefined variables. 

@vladikoff Would you like to keep a strict interpretation of the rule: changing `var ast, compiled, filename` to separate `var` statements? Or should the JSCS rule be amended to exclude undefined variables? I'd lean toward the second option and include the amended rule as part of the Grunt preset.