FlxTrailArea fixes

Hi there folks, I've made some changes to FlxTrailArea to fix the problems related in issue https://github.com/HaxeFlixel/flixel/issues/832 
I'm not sure if there are the correct changes, need a haxeflixel guru review them :)
Changes made:
- Don't rotate or scale the sprite if the original one isn't scaled or rotated.
- Use the origin of the sprite and not the middle for rotate and scale calculations.
-  Fix Neko/cpp crashes by getting the FlxFrame BitmapData.