Allow the matcher provide a custom error message

src/core/Expectation.js

@@ -65,6 +65,7 @@ getJasmineRequireObj().Expectation = function() {
           matcherName: name,
           passed: result.pass,
           message: message,
+          error: result.error,
           actual: this.actual,
           expected: expected // TODO: this may need to be arrayified/sliced
         }