Merge branch 'sam_process_headers_improvement' into sam_2134_base
Made transition_timestamp_t be cluster-serializable.

Thus showing that it is not stored on disk.
Made fifo enforcers not use transition_timestamp_t.
Removed some trailing whitespace.
Merge branch 'next' into sam_timestamps_with_a_vengeance
Got rid of transition_timestamp_t::to_repli_timestamp.  Made callers change behavior, calling timestamp_after.

Probably a bugfix if not an introduction of a bug.
Made store_view_t (and store_t, etc) use state_timestamp_t.
Made listener not use transition_timestamp_t.
Made broadcaster not use transition_timestamp_t.
Removed transition_timestamp_t from unittests.
Changed some variable names.
Removed the unused transition_timestamp_t type.
Made state_timestamp_t::pred be debug-only (just because we can).
Removed dumb txn_t-constructing repli_timestamp_t::invalid uses in btree_store.cc.
Removed uses of repli_timestamp_t::invalid in btree directory.
Simplify rdb_backfill_chunk_get_btree_repli_timestamp_visitor_t a bit.
Moved max_inserted_repli_timestamp, which is really txn_t-specific logic, local to store_t::receive_backfill.
Made members of backfill_chunk_timestamp_t, moved in the previous commit, be const.
Removed repli_timestamp-t::invalid usage everywhere outside of the cache and serializer.
Made txn_t constructor guarantee that it is not passed an invalid timestamp.