Fix special IE property parsing

Fixes issue #683 - Parsing issues with IE specific property syntax.

The whole ie specific property is parsed as a whole (as it was before), but now it should do it with a proper "parsing tree". This is IMO not a 100% proper fix, since all tokens should be parsed and emmitted as such, so they would ie. generate source-map entries. But this is a nice start, since it now recognizes the tokens as such, it just doesn't create an "AST tree".

@xzyfer What do you think?