Avoid the use of .caught(...) on promises that we didn't necessarily …

…create ourselves.

Fixes unexpected-promise with non-Bluebird promises (reporter by Munter via Gitter).

lib/Unexpected.js

@@ -652,8 +652,8 @@ Unexpected.prototype.expect = function expect(subject, testDescriptionString) {
             var callInNestedContext = function (callback) {
                 try {
                     var result = oathbreaker(callback());
-                    if (result && typeof result.then === 'function' && typeof result.caught === 'function') {
-                        return result.caught(function (e) {
+                    if (result && typeof result.then === 'function') {
+                        return result.then(undefined, function (e) {
                             if (e && e._isUnexpected) {
                                 truncateStack(e, wrappedExpect);
                                 throw handleNestedExpects(wrappedExpect, e, assertion);
@@ -793,7 +793,7 @@ Unexpected.prototype.expect = function expect(subject, testDescriptionString) {
     try {
         var promise = executeExpect(subject, testDescriptionString, args);
         if (promise && typeof promise.then === 'function') {
-            return promise.caught(function (e) {
+            return promise.then(undefined, function (e) {
                 if (e && e._isUnexpected) {
                     // TODO truncate the stack
                     that.setErrorMessage(e);
@@ -857,7 +857,7 @@ Unexpected.prototype.async = function (cb) {
         result.then(function () {
             that._isAsync = false;
             done();
-        }).caught(function (err) {
+        }, function (err) {
             that._isAsync = false;
             done(err);
         });