Fixed the Doxygen config to ignore __attribute() annotations
Turn off SQLite shared-cache mode

Backs out part of commit f12e420 from Nov. 6.
Shared-cache mode has some very disruptive effects on concurrency
if one connection is stepping through query results while another connection
tries to make changes.
See http://thread.gmane.org/gmane.comp.db.sqlite.general/73960
Fixes #189 (and possibly other recent regressions?)
Make -[CBLDatabase doSync:] public

This method is dangerous (will deadlock if called on the CBLManager’s
thread/queue) but useful for apps using GCD.