Enable partially passing libsass spec tests (#1488)

Merge pull request #1480 from mgreter/activate-passing-libsass-todo

Activate passing libsass todo spec tests

Add test for `:not(&-c)`

Refs sass/libsass#2630

3.5.4

3.5.3

3.5.1

3.5.0

3.5.0-2

3.5.0-1

3.5.0-0