[qmf] Fix double emiting of messageUpdate/messageAdded signal.

Double emition was introduced by this commit:
https://qt.gitorious.org/qt-labs/messagingframework/commit/9aca2eb83a164d3da4bce635eca58e9f3751ca95
When data or properties are updated in the store instance respective messageUpdate/messageAdded signals
are already emitted.
Not really, since in normal usage it would come from the network, we only have UT's to check the signals for local changes only, this is not the first time similar problem happens(UTs also in this commit): https://qt.gitorious.org/qt-labs/messagingframework/commit/199908c8a14e78e98e65f229e6f4b48446bf41b2

I think I can create UT's if I use two different processes accessing the store(not sure how robust this will be for the test framework), this way I can catch signals the same way it would be done if messages were added from the network via one of the plugins. If there's a better or simpler way please let me know.