Per specs, an out of bound WINDOWSIZE defaults to 512, not 100.
This is really a global limit, not a default.

Also, add method to retrieve the value as well.
We shouldn't need to override this.
Per specs, when any WINDOWSIZE is omitted it defaults to 100.
Perform WINDOWSIZE/MOREAVAILABLE logic in Horde_ActiveSync_Request_Sync::.

Now correctly checks for collection level WINDOWSIZE as well as the
global WINDOWSIZE values. Stopping output once either is reached.