Fixing a few errors, adding support for attributedPlaceholder

Look at the code before and after. Before, we weren't rejecting notifications that were generated by objects other than ourselves, now we are.

You can see the effectiveness by putting say `NSLog(@"0x%x UITextFieldTextDidChangeNotification");` in this function. Without the check, you'll see all of the existing `UIFloatLabelTextField`s do something with the notification. With the check, only the `UIFloatLabelTextField` which actually had some text change will do something.

It may well have worked in the sample app, but it is definitely incorrect.