Adding a spec test for nested selector groups that have combinators. Still passes!

spec/basic/09_selector_groups_and_combinators/input.scss

+a + b, c {
+  blah: blah;
+  bleh: bleh;
+  d e, f ~ g + h {
+    bloo: bloo;
+    blee: blee;
+  }
+}
\ No newline at end of file

spec/basic/09_selector_groups_and_combinators/output.css

+a + b, c {
+  blah: blah;
+  bleh: bleh; }
+  a + b d e, a + b f ~ g + h, c d e, c f ~ g + h {
+    bloo: bloo;
+    blee: blee; }