Sub-transaction bugfixes

* Sub-transaction bugfix: When sub transaction wasnt used, it would
resolve after main transaction gone inactive.

* Other bugfix for Dexie.Observable: Dexie.Observable could
theoretically miss changes from a sub transaction.
Bugfix chained listeners on('ready')

Bug if having multiple listeners to on('ready').
Bugfixes Observable and Syncable

Bug fixes to the plugins Dexie.Observable.js and Dexie.Syncable.js.
Bugfix Dexie.Syncable

Prior bugfix made Dexie.Syncable bail out when syncing items initial
time. All objects from the server were put into the first table even for
objects belonging to other tables.
Bugfixed unit tests

Two transaction unit tests sometimes stalled forever when Dexie.Syncable
and Dexie.Observable were applied. Reason was that the tests did
db2.delete() twice when finished. This could make a later unit test fail
to open db2 again since the two delete() operations could potentially
block each other.