btn:hover effect doesn't work in IE

[jmchambers]

Hi, I noticed that there is no mouse-over effect on btn-primary in IE8, but this works if I use the precompiled bootstrap.css. So I started digging...

I compared the css and found that the button's background colour is different in the compass generated css. This is happening because of a small difference between mixins.less and mixins.scss. The less version uses the sass mix() function for gradient-vertical and gradient-vertical-three-colors, while the scss version doesn't.

If I've understood the build process correctly, mixins is the only file that doesn't get auto-magically ported..? So, I've forked and corrected it and will make a pull request shortly...

Cheers.

P.S. thanks for making this gem - it's awesome