Fix for when transformer block rejects a pulled doc

Needed to mark the doc's sequence as no longer pending. Otherwise the
checkpoint doesn't advance, and the puller will keep trying to pull that
doc on subsequent runs.
Fixed another assertion-failure when a _bulk_get download can’t parse a JSON doc

Found a piece that was missing from the prior fix 24f6381. The same assertion failure was occurring,
under slightly different circumstances.
Fixes #288 (speculatively). Also see #271, #232.
Tweaked some logging in CBLReplication.m.