Pixel units explicitly declared don't seems to work anymore

[cbchouinard]

When explicitly using the pixel unit in constraints declaration I have this error:

Undefined command: px called as px(200)

Check the code pen:
http://codepen.io/cbchouinard/pen/wBeOJd

I've added some test on the ccss-compiler which shows that the ast is correctly generated by the ccss-compiler when using the pixel unit:
https://github.com/gss/ccss-compiler/tree/pixel-unit-explicititly-declared-in-constraints

[cbchouinard]

Also have the same exception with the following units:

cm, mm, in

[Inviz]

Should be fixed on 2.1.x branch