domain: run now return callback result

both domain.bind and domain.intercept act this way

lib/domain.js

@@ -136,7 +136,7 @@ Domain.prototype.remove = function(ee) {
 };
 
 Domain.prototype.run = function(fn) {
-  this.bind(fn)();
+  return this.bind(fn)();
 };
 
 Domain.prototype.intercept = function(cb) {

test/simple/test-domain.js

@@ -199,6 +199,10 @@ d.run(function() {
   });
 });
 
+var result = d.run(function () {
+  return 'return value';
+});
+assert.equal(result, 'return value');
 
 
 var fst = fs.createReadStream('stream for nonexistent file')