VML: opacity for second color stop in gradient

[isadovskiy]

VML supports opacity2 property (http://msdn.microsoft.com/en-us/library/bb229613(v=vs.85).aspx). Which allows to configure opacity for the second color stop in gradient. I see it's still not supported with Raphael.

I implemented fix some time ago which adds support for this property. I will create pull request for within next couple of days.