Remove bogus executable permissions on xlog.c.

Apparently fat-fingered in 1a3d104475ce01326fc00601ed66ac4d658e37e5.
Noted by Peter Geoghegan.
Display old and new values in pg_resetxlog -n output.

For extra clarity.

Rajeev Rastogi, reviewed by Amit Kapila
Fix progress logging when scale factor is large.

Integer overflow showed minus percent and minus remaining time something like this.
  239300000 of 3800000000 tuples (-48%) done (elapsed 226.86 s, remaining -696.10 s).
Allow time delayed standbys and recovery

Set min_recovery_apply_delay to force a delay in recovery apply for commit and
restore point WAL records. Other records are replayed immediately. Delay is
measured between WAL record time and local standby time.

Robert Haas, Fabrízio de Royes Mello and Simon Riggs
Detailed review by Mitsumasa Kondo
New autovacuum_work_mem parameter

If autovacuum_work_mem is set, autovacuum workers now use
this parameter in preference to maintenance_work_mem.

Peter Geoghegan
Improve EXPLAIN to print the grouping columns in Agg and Group nodes.

Per request from Kevin Grittner.
Fix ancient docs/comments thinko: XID comparison is mod 2^32, not 2^31.

Pointed out by Gianni Ciolli.