Added assertion about write txn_t being constructed with repli_timestamp_t::invalid.
Made btree_store_t<>::set_metainfo use distant_past instead of invalid.
Made btree_store_t<>::reset_data use distant_past.
Revert "Made btree_store_t<>::reset_data use distant_past."

This reverts commit 7d06dcaf5cd08a3970738508ac95ff57984b7764.
Revert "Made btree_store_t<>::set_metainfo use distant_past instead of invalid."

This reverts commit 9372baf6b95d840504a91bdcc9f0c7ce6a3861fe.
Made txn_t constructor convert invalid timestamp to distant_past.