SQLStore.put() assumes that at least one field is dirty

[jnioche]

if not - we end up with an incorrect SQL query e.g.

INSERT INTO webpages (id )VALUES ('uk.co.bbc.news:http/sport2/hi/video_and_audio/default.stm') ON DUPLICATE KEY UPDATE ;

where nothing follows the update

[dogacan]

Fixed at 8971b6a .

Also added a test case.

There is a larger problem that still remains unsolved:

T obj = dataStore.get(key);
dataStore.put(anotherKey, obj)

If you do this, Gora will not write anything under anotherKey since obj has no dirty fields. I propose that we store the original key for a Persistent object in its StateManager. If then, someone tries to store it under another key, data store will realize it and write ALL fields whether dirty or not.