Opt for better handling of keyName.

Attempt to infer the keyName from the name of the function, however in
that absence, pass down the parentKeyName.

Author: tbranyen

index.js

@@ -46,7 +46,7 @@ function processExports(exports, test, cached, parentKeyName) {
     // is asynchronous.
     if (test) {
       // Pass the function itself, its keyName, and the parent keyName.
-      if (!test(exports, keyName, parentKeyName)) {
+      if (!test(exports, exports.name || parentKeyName)) {
         return exports;
       }
     }

test/index.js

@@ -98,8 +98,8 @@ describe("Promisify", function() {
         a: function a() { arguments[0](); }
       };
 
-      promisify(Test, function(func, keyName, parentKeyName) {
-        return func.name === "a";
+      promisify(Test, function(func, keyName) {
+        return keyName === "a";
       });
 
       return new Test().a();