Better support for @-moz-document

[xzyfer]

There are cases where we error when handling @-moz-document for example

@-moz-document url-prefix(http://sass-lang.com/docs) {
  .foo { a: b; }
}

Produces the following error

Error: expected a variable name (e.g. $x) or ')' for the parameter list for url-prefix
        on line 1 of test.scss
>> @-moz-document url-prefix(http://sass-lang.com/docs) {
   --------------------------^

Spec sass/sass-spec#460
Spec https://github.com/sass/sass-spec/tree/master/spec/libsass-todo-tests/scss-tests/127_test_moz_document_interpolation

[xzyfer]

Handling of url-prefix has been fixed in #1466. There remaining aspect of @-moz-document support are outstanding.

[mgreter]

As I see it the only difference left is that we do not preserve line-feeds and spaces inside the list. Quite possible that there are other lists where we should preserve white-space!? Maybe want to close this and open a new one?

[mgreter]

This might be fixed by #1868 (partially, the issue in this ticket is ok)

[mgreter]

Closing in favor of #1596

[Designer023]

Just a note for anyone who needs a workaround before the updated version is released (or is stuck on an old version) can try the following:

#{ '@-moz-document \url-prefix()' } {  ...  }