doc: Explain that ereport doesn't return for ERROR or higher levels.

Christophe Pettus
Fix some "translator:" comments mangled by pgindent
Initialize cached OID to Invalid in new hash entries

Andres Freund; bug detected by valgrind
Accept multiple -I, -P, -T and -n options in pg_restore.

We already did this for -t (--table) in 9.3, but missed the other similar
options. For consistency, allow all of them to be specified multiple times.

Unfortunately it's too late to sneak this into 9.3, so commit to master
only.
Partially restore comments discussing enum renumbering hazards.

As noted by Tom Lane, commit 813fb0315587d32e3b77af1051a0ef517d187763
was overly optimistic about how safe it is to concurrently change
enumsortorder values under MVCC catalog scan semantics.  Restore
some of the previous text, with hopefully-correct adjustments for
the new state of play.
Allow discovery of whether a dynamic background worker is running.

Using the infrastructure provided by this patch, it's possible either
to wait for the startup of a dynamically-registered background worker,
or to poll the status of such a worker without waiting.  In either
case, the current PID of the worker process can also be obtained.
As usual, worker_spi is updated to demonstrate the new functionality.

Patch by me.  Review by Andres Freund.
Alvaro's review patch for Extension Templates (v4)
Properly init extension's template schema when it was not provided by the user.
Restrict Extension Templates to superusers.
Fix the hstore Makefile.
Fix Extension Template renaming to enforce the same rules as the creation of them.
Fix the SGML markups so that we can compile the docs.
Add some contents to the docs.
More cleaning and rebasing.
Add support for Extension Template OWNER in pg_dump.
Cleanup the hstore default_full_version edits.
Fix all infelicities and bugs reported in the current review.
Error out when trying to alter a non-existing template (rename, owner).
Remove an old limitation text in the docs, per Markus' review.
Fix a useless diff, per Markus.