Abort concatenating stylesheet containing @import

[westonruter]

@import statements must be at the beginning of a stylesheet, so the stylesheet is concatenated with another, it will fail.

[topher1kenobe]

Are you thinking we should test for this case and magically enqueue, or simply throw an error?

[westonruter]

Throw an error.

[msigley]

I have written a fork that adds at rule handling to the concatenation.
#60