disable conversation cursor network access during iteration

ViewPager needs to iterate through the conversation cursor to
match up fragments and cursor rows. Prevent its iterating from
having side effects like unintended network access by signaling
to the underlying cursor that network access should be
temporarily turned off.

Support on the Gmail provider side will be added in an
accompanying CL.

Change-Id: I05231815de53423ff024fc85a59806ddbaa200a6
4 files changed