PropertyHandlerMapping should allow unprefixed names

Currently PropertyHandlerMapping will always register method names with the form "<pKey>.<methodname>", there is no way to create a method without prefix. Even when pKey is null, the name generated will be "null.<methodname>".

Similiar to the recent change on the client side, I propose to change name generation to not generate a prefix if pKey is null, e.g. in registerPublicMethods():

String name=(pKey!=null)?(pKey + "." + method.getName()):method.getName();