Fix Issue with fa-rotate-* in IE9 #3527

Issue related with IE9 : fa-rotate-* not work correctly ;/ (css filter and -ms-transform)
Solution is add:
:root .@{fa-css-prefix}-rotate-90,
:root .@{fa-css-prefix}-rotate-180,
:root .@{fa-css-prefix}-rotate-270,
:root .@{fa-css-prefix}-flip-horizontal,
:root .@{fa-css-prefix}-flip-vertical {
  filter: none;
}

Tested on IE 8:
![ie8](https://cloud.githubusercontent.com/assets/4445155/3088952/4ddecb42-e578-11e3-8a4d-80dbf53473c1.jpg)
Tested on IE 9:
![ie9](https://cloud.githubusercontent.com/assets/4445155/3088953/4ddfc5e2-e578-11e3-99bf-15d2ba38bacd.jpg)
Tested on IE 10:
![ie10](https://cloud.githubusercontent.com/assets/4445155/3088954/4de45ea4-e578-11e3-9ec5-eeca6152c734.jpg)

Similar issue - resolved:
https://github.com/paulirish/css3please/issues/73