Fix pg_rewind when pg_xlog is a symlink.

Heikki Linnakangas <heikki.linnakangas@iki.fi>

Commit: 615b69595525385bbf050a170912b7671cacc5c8
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: 2015-08-03T12:25:12Z
Releases: 9.5.0
Fix pg_rewind when pg_xlog is a symlink.

pg_xlog is often a symlink, typically to a different filesystem. Don't
get confused and comlain about by that, and just always pretend that it's a
normal directory, even if it's really a symlink.

Also add a test case for this.

Backpatch to 9.5.

Files