Allow reindex count to differ from old count

This is required because we reindex while handling live traffic.  We
should be doing a forceSearchIndex after each in place reindex over the
time of the reindex to catch up.  I've added documentation to that
effect.

Change-Id: I55b3f21d6ddff8cdd7325d00cb67d25487d6ecb4
Merge "Allow reindex count to differ from old count"