Added mongoc_cursor_get_batch_size() and mongoc_cursor_set_batch_size()

The batch size needs to be tweakable between getmores
Add mongoc_client_kill_cursor()

A good samaritan should clean after himself using
mongoc_cursor_destroy(cursor), but you may not always have the cursor instance.
You are just trying to cleanup after a broken process, and all you got is
the cursorid, which you retrieved from db.currentOp()
Add mongoc_cursor_get_id()

These can be retrieved by calling currentOp, but its impossible to map
them to specific cursor. We can just as well expose the id rather then
having the user guessing
Missing entry macro

Was interesting seeing tracing leaving a function it didn't enter