Use /etc/localtime to identify system timezone when possible

When Who What
2018-09-13 16:36:47 Tom Lane (tgl) Closed in commitfest 2018-09 with status: Committed
2018-09-13 16:01:51 Tom Lane (tgl) Changed reviewers to Michael Paquier (michael-kun)
2018-09-13 16:01:00 Tom Lane (tgl) Added tgl as committer
2018-09-12 22:44:35 Michael Paquier (michael-kun) New status: Ready for Committer
2018-08-10 22:14:20 Andrew Dunstan (adunstan) Closed in commitfest 2018-07 with status: Moved to next CF
2018-06-01 15:28:27 Gerdan Santos (gerdan) Added gerdan as reviewer
2018-05-10 23:25:13 Tom Lane (tgl) Added annotation "patch v1 here" to 21138.1525969099@sss.pgh.pa.us
2018-05-10 23:24:02 Tom Lane (tgl) Changed authors to Tom Lane (tgl)
2018-05-10 23:23:43 Tom Lane (tgl) Attached mail thread 30896.1492006367@sss.pgh.pa.us
2018-05-10 23:23:42 Tom Lane (tgl) Created patch record