Duplicate alpha unmultiplication

Nobody has claimed this yet.

The version posted on quasimondo.com has a bug that has already been fixed elsewhere. Specifically, the RGB values are multiplied by inverse alpha in lines 213-219, and again in lines 322-328. This produces strange artifacts in translucent areas. The unmultiplication should only be applied on the second pass, so the first pass can be simplified for a little extra speed boost.

I submitted this fix to Mario Klingemann recently, and he informed me that it had already been fixed in EaselJS, but not yet back-ported to his own version. The one in EaselJS has some other nice features too, like independent `blurX` and `blurY` parameters for anisotropic blur, and a `quality` parameter to control the iterations of stack depth. Check it out:

https://github.com/CreateJS/EaselJS/blob/master/src/easeljs/filters/BlurFilter.js

I'm looking for a stand-alone version of this without the EaselJS dependency. If I can't find one, I guess I'll do it myself.

Compare the standalone implementation's first-pass logic at lines 213-219 with the second pass at lines 322-328, then review the linked EaselJS BlurFilter.js implementation. Done means removing the duplicate unmultiplication from the first pass while preserving the second-pass behavior and standalone use without the EaselJS dependency.

Written by the indexing model from the issue text.