psql:  update "replica identity" display for \d+

Display "replica identity" only for \d plus mode, exclude system schema
objects, and display all possible values, not just non-default,
non-index ones.
Pass more than the first XLogRecData entry to rm_desc, with WAL_DEBUG.

If you compile with WAL_DEBUG and enable it with wal_debug=on, we used to
only pass the first XLogRecData entry to the rm_desc routine. I think the
original assumprion was that the first XLogRecData entry contains all the
necessary information for the rm_desc routine, but that's a pretty shaky
assumption. At least standby_redo didn't get the memo.

To fix, piece together all the data in a temporary buffer, and pass that to
the rm_desc routine.

It's been like this forever, but the patch didn't apply cleanly to
back-branches. Probably wouldn't be hard to fix the conflicts, but it's
not worth the trouble.