Fix duplicate promise rejections.

We can just reuse chained dispatched rejected promises.

The test was also broken; it needs to check for emptiness after fail()
runs.

Fixes kriskowal#238.

CHANGES.md

@@ -5,6 +5,7 @@
  - `isPromise` and `isPromiseAlike` now always returns a boolean 
    (even for falsy values). #284 @lfac-pt
  - Support for ES6 Generators in `async` #288 @andywingo
+ - Clear duplicate promise rejections from dispatch methods #238 @SLaks
 
 ## 0.9.3
 

q.js

@@ -791,7 +791,7 @@ function reject(reason) {
             return rejected ? rejected(reason) : this;
         }
     }, function fallback() {
-        return reject(reason);
+        return this;
     }, function valueOf() {
         return this;
     }, reason, true);

spec/q-spec.js

@@ -2423,10 +2423,10 @@ describe("unhandled rejection reporting", function () {
     });
 
     it("doesn't report when you chain off a rejection", function () {
-        Q.reject("this will be handled").get("property").fail(function () {
+        return Q.reject("this will be handled").get("property").fail(function () {
             // now it should be handled.
+        }).fin(function() {
+            expect(Q.unhandledReasons.length).toEqual(0);
         });
-
-        expect(Q.unhandledReasons.length).toEqual(0);
     });
 });