[PATCH 6/8] Log enough data into the wal to reconstruct logical changes from it if wal_level=logical

This adds a new wal_level value 'logical'

Missing cases:
- heap_multi_insert
- primary key changes for updates
- no primary key
- LOG_NEWPAGE
---
 src/backend/access/heap/heapam.c        | 135 +++++++++++++++++++++++++++++---
 src/backend/access/transam/xlog.c       |   1 +
 src/backend/catalog/index.c             |  74 +++++++++++++++++
 src/bin/pg_controldata/pg_controldata.c |   2 +
 src/include/access/xlog.h               |   3 +-
 src/include/catalog/index.h             |   4 +
 6 files changed, 207 insertions(+), 12 deletions(-)