Fixes to GenerateFrameNumbers
Fixes to GenerateFrameNumbers

* `GenerateFrameNumbers` would include the __BASE frame by mistake in its calculations. This didn't end up in the final animation, but did cause a cache miss when building the animation.
* `GenerateFrameNumbers` can now accept the `start` and `end` parameters in reverse order, meaning you can now do `{ start: 10, end: 1 }` to create the animation in reverse.

photonstorm/phaser,spayton/phaser,spayton/phaser,BeanSeed/phaser,BeanSeed/phaser,photonstorm/phaser