Add test for nested media query logical combination

Nesting media queries combines queries in a manner similar to nesting selectors, but with some logical evaluation of the parameters. 

In the test example the repetition of `screen` is taken in to account, while the logically conflicting `print` declaration is left out, and `min-width`/`max-width` queries are combined with `and`.

https://github.com/sass/libsass/issues/185