more care around generated names, fixes #60 #82 and #97

test/codegen/expect/methods.js

 var methods;
 (function(exports) {
   'use strict';
   let _c = Symbol('_c');
   class A extends core.Object {
     A() {
       this[_c] = 3;
     }
     x() {
       return 42;
     }
     y(a) {
       return a;
     }
     z(b) {
       if (b === void 0)
         b = null;
       return b;
     }
     zz(b) {
       if (b === void 0)
         b = 0;
       return b;
     }
-    w(a, opt$) {
-      let b = opt$ && 'b' in opt$ ? opt$.b : null;
+    w(a, opts) {
+      let b = opts && 'b' in opts ? opts.b : null;
       return dart.notNull(a) + dart.notNull(b);
     }
-    ww(a, opt$) {
-      let b = opt$ && 'b' in opt$ ? opt$.b : 0;
+    ww(a, opts) {
+      let b = opts && 'b' in opts ? opts.b : 0;
       return dart.notNull(a) + dart.notNull(b);
     }
     get a() {
       return this.x();
     }
     set b(b) {}
     get c() {
       return this[_c];
     }
     set c(c) {
@@ skipping 14 matching lines @@
   function test() {
     let f = new Foo();
     dart.dinvoke(f, 'bar', "Bar's call method!");
   }
   // Exports:
   exports.A = A;
   exports.Bar = Bar;
   exports.Foo = Foo;
   exports.test = test;
 })(methods || (methods = {}));