Support for native in leg, and start moving native tests to a specific test suite.

frog/leg/ssa/codegen.dart

Index: frog/leg/ssa/codegen.dart
===================================================================
--- frog/leg/ssa/codegen.dart	(revision 4390)
+++ frog/leg/ssa/codegen.dart	(working copy)
@@ -536,7 +536,11 @@
       }
       code = code.replaceAll('\$$i', name);
     }
-    buffer.add('($code)');
+    if (node.generateAtUseSite()) {
+      buffer.add('($code)');
+    } else {
+      buffer.add('$code');
+    }
   }
 
   visitForeignNew(HForeignNew node) {