[Bf-committers] Adding weight preview to vgroup modifiers

[Bastien Montagne]

Hi devs,

Here is the codereview link to the patch corresponding to current 
vgroup_modifiers branch: http://codereview.appspot.com/5531047/

It:
*Slightly enhances the weight preview behavior for modifiers using it 
(esp. in the WeightPaint mode, where it allows to either see the org 
weight, final weight, or modifier preview).
*Adds weight preview to the vgroup modifiers.

Tests and comments are very welcome! :)

Cheers,
Bastien