employ a better parser for command-line arguments

to support passing commas in strings in for example:

    uglifyjs2 -cd TEST="'a,b'" <<EOF
    console.log(TEST);
    EOF

    → console.log("a,b")

close #14

lib/compress.js

@@ -134,6 +134,17 @@ merge(Compressor.prototype, {
     };
 
     function make_node_from_constant(compressor, val, orig) {
+        // XXX: WIP.
+        // if (val instanceof AST_Node) return val.transform(new TreeTransformer(null, function(node){
+        //     if (node instanceof AST_SymbolRef) {
+        //         var scope = compressor.find_parent(AST_Scope);
+        //         var def = scope.find_variable(node);
+        //         node.thedef = def;
+        //         return node;
+        //     }
+        // })).transform(compressor);
+
+        if (val instanceof AST_Node) return val.transform(compressor);
         switch (typeof val) {
           case "string":
             return make_node(AST_String, orig, {