Adds IE test for css expressions

IE expressions are not parsed. Example is taken from:
http://msdn.microsoft.com/en-us/library/ms537634%28v=vs.85%29.aspx

Fixed by commit: https://github.com/mgreter/libsass/commit/691e1012a3e7cdf4484f60bc3f5a01a9e6800ac6
Pending in pull request https://github.com/hcatlin/libsass/pull/181

Tested via [CSS::Sass](https://github.com/mgreter/CSS-Sass) https://github.com/mgreter/CSS-Sass/commit/91884f018f5bf7d69e0c61b1ecb7b3477fe732cf