fix mangling collision with keep_fnames (#1431)

* fix mangling collision with keep_fnames
fixes #1423

* pass mangle options to figure_out_scope()
bring command-line in line with minify()

test/input/issue-1431/sample.js

@@ -0,0 +1,14 @@
+function f(x) {
+    return function() {
+        function n(a) {
+            return a * a;
+        }
+        return x(n);
+    };
+}
+
+function g(op) {
+    return op(1) + op(2);
+}
+
+console.log(f(g)() == 5);