stylo: Fix and ensure alignment of restyle hints. Test it on Travis.

Turns out eRestyle_LaterSiblings was not really matching, sigh...

python/servo/testing_commands.py

@@ -158,6 +158,17 @@ class MachCommands(CommandBase):
                     return suite
         return None
 
+    @Command('test-geckolib',
+             description='Test geckolib sanity checks',
+             category='testing')
+    def test_geckolib(self):
+        self.ensure_bootstrapped()
+
+        env = self.build_env()
+        env["RUST_BACKTRACE"] = "1"
+
+        return call(["cargo", "test"], env=env, cwd=path.join("ports", "geckolib"))
+
     @Command('test-unit',
              description='Run unit tests',
              category='testing')