Remove single space on end of a line in xlog.c

Michael Paquier
Emit msg correctly for timeline-crossing crash
Init crash recovery using the latest available TLI

This simplifies the handling of crashes after fast promotion and various
minor cases that can exist in short timing windows around that case.

Broad fix to bug reported by Michael Paquier on -hackers,
approach prompted by Heikki Linnakangas
Clarify documentation of EXPLAIN (TIMING OFF) option.

Clarify that this option doesn't suppress measurement of the statement's
total runtime.

Greg Smith