We recently added flagging_create(), so we're in line with Entity API.

However, the flag class already had a new_flagging() method -- just I for one didn't know about it.

While flagging_create() fits the Entity API pattern of having an entity create callback, the method on the flag is quite handy too for use within the flag class.

Therefore, flagging_create() should call $flag->new_flagging(). new_flagging() should be extended to behave more like a standard entity creation function.