Actually let's move away those monsters from the evaluate function

ev() should do a single thing — evaluate constant expressions.  if that's
not possible, just return the original node.  it's not the best place for
partial evaluation there, instead doing it in the compress functions.

test/compress/arrays.js

@@ -69,6 +69,6 @@ constant_join_2: {
         var e = [ "foo", "bar", boo(),
                   "foo+1+2+3+bar",
                   "baz", "x", "y" ].join("really-long-separator");
-        var f = "str" + ("str" + variable) + "foobar" + ("moo" + foo);
+        var f = "strstr" + variable + "foobar" + ("moo" + foo);
     }
 }