adjusted css3 prefixing for background gradients to a) increase browser support for standard prefixed gradients, and b) remove -ms filter gradients due to a rendering issue in IE9 that conflicts with border radius. Gradient support is set for IE10, however. More info on this bug and decision can be found at issue #2046. Fixes #2046. Fixes #1933. Addresses a portion of #13 as well.

Author: scottjehl