Clarify terminology standalone backend vs. single-user mode

Most of the documentation uses "single-user mode", so use that in the
code as well.  Adjust the documentation to match the new error message
wording.  Also add a documentation index entry for "single-user mode".

Based-on-patch-by: Jeff Janes <jeff.janes@gmail.com>
doc: Fix date in EPUB manifest

If there is no <date> element, the publication date for the EPUB
manifest is taken from the copyright year.  But something like
"1996-2013" is not a legal date specification.  So the EPUB output
currently fails epubcheck.

Put in a separate <date> element with the current year.  Put it in
legal.sgml, because copyright.pl already instructs to update that
manually, so it hopefully won't be missed.
Ensure no xid gaps during Hot Standby startup

In some cases with higher numbers of subtransactions
it was possible for us to incorrectly initialize
subtrans leading to complaints of missing pages.

Bug report by Sergey Konoplev
Analysis and fix by Andres Freund
Add a comment warning against use of pg_usleep() for long sleeps.

Follow-up to commit 873ab97219caabeb2f7b390268a4fe01e2b7518c, in which
I noted that WaitLatch was a better solution in the commit log message,
but neglected to add any documentation in the code.
Translation updates
ALTER TABLE ... ALTER CONSTRAINT for FKs

Allow constraint attributes to be altered,
so the default setting of NOT DEFERRABLE
can be altered to DEFERRABLE and back.

Review by Abhijit Menon-Sen
Reverting previous commit, pending investigation
of sporadic seg faults from various build farm members.
Support clean switchover.

In replication, when we shutdown the master, walsender tries to send
all the outstanding WAL records to the standby, and then to exit. This
basically means that all the WAL records are fully synced between
two servers after the clean shutdown of the master. So, after
promoting the standby to new master, we can restart the stopped
master as new standby without the need for a fresh backup from
new master.

But there was one problem so far: though walsender tries to send all
the outstanding WAL records, it doesn't wait for them to be replicated
to the standby. Then, before receiving all the WAL records,
walreceiver can detect the closure of connection and exit. We cannot
guarantee that there is no missing WAL in the standby after clean
shutdown of the master. In this case, backup from new master is
required when restarting the stopped master as new standby.

This patch fixes this problem. It just changes walsender so that it
waits for all the outstanding WAL records to be replicated to the
standby before closing the replication connection.

Per discussion, this is a fix that needs to get backpatched rather than
new feature. So, back-patch to 9.1 where enough infrastructure for
this exists.

Patch by me, reviewed by Andres Freund.
Properly dump dropped foreign table cols in binary-upgrade mode.

In binary upgrade mode, we need to recreate and then drop dropped
columns so that all the columns get the right attribute number. This is
true for foreign tables as well as for native tables. For foreign
tables we have been getting the first part right but not the second,
leading to bogus columns in the upgraded database. Fix this all the way
back to 9.1, where foreign tables were introduced.
Avoid inconsistent type declaration

Clang 3.3 correctly complains that a variable of type enum
MultiXactStatus cannot hold a value of -1, which makes sense.  Change
the declared type of the variable to int instead, and apply casting as
necessary to avoid the warning.

Per notice from Andres Freund
pg_receivexlog: Fix logic error

The code checking the WAL file name contained a logic error and wouldn't
actually catch some bad names.
Merge branch 'master' into ordinality