Disallow pushing volatile qual expressions down into DISTINCT subqueries.

A WHERE clause applied to the output of a subquery with DISTINCT should
theoretically be applied only once per distinct row; but if we push it
into the subquery then it will be evaluated at each row before duplicate
elimination occurs.  If the qual is volatile this can give rise to
observably wrong results, so don't do that.

While at it, refactor a little bit to allow subquery_is_pushdown_safe
to report more than one kind of restrictive condition without indefinitely
expanding its argument list.

Although this is a bug fix, it seems unwise to back-patch it into released
branches, since it might de-optimize plans for queries that aren't giving
any trouble in practice.  So apply to 9.4 but not further back.
Fix broken Assert() introduced by 8e9a16ab8f7f0e58

Don't assert MultiXactIdIsRunning if the multi came from a tuple that
had been share-locked and later copied over to the new cluster by
pg_upgrade.  Doing that causes an error to be raised unnecessarily:
MultiXactIdIsRunning is not open to the possibility that its argument
came from a pg_upgraded tuple, and all its other callers are already
checking; but such multis cannot, obviously, have transactions still
running, so the assert is pointless.

Noticed while investigating the bogus pg_multixact/offsets/0000 file
left over by pg_upgrade, as reported by Andres Freund in
http://www.postgresql.org/message-id/20140530121631.GE25431@alap3.anarazel.de

Backpatch to 9.3, as the commit that introduced the buglet.
Don't allow relminmxid to go backwards during VACUUM FULL

We were allowing a table's pg_class.relminmxid value to move backwards
when heaps were swapped by VACUUM FULL or CLUSTER.  There is a
similar protection against relfrozenxid going backwards, which we
neglected to clone when the multixact stuff was rejiggered by commit
0ac5ad5134f276.

Backpatch to 9.3, where relminmxid was introduced.

As reported by Heikki in
http://www.postgresql.org/message-id/52401AEA.9000608@vmware.com
Have multixact be truncated by checkpoint, not vacuum

Instead of truncating pg_multixact at vacuum time, do it only at
checkpoint time.  The reason for doing it this way is twofold: first, we
want it to delete only segments that we're certain will not be required
if there's a crash immediately after the removal; and second, we want to
do it relatively often so that older files are not left behind if
there's an untimely crash.

Per my proposal in
http://www.postgresql.org/message-id/20140626044519.GJ7340@eldon.alvh.no-ip.org
we now execute the truncation in the checkpointer process rather than as
part of vacuum.  Vacuum is in only charge of maintaining in shared
memory the value to which it's possible to truncate the files; that
value is stored as part of checkpoints also, and so upon recovery we can
reuse the same value to re-execute truncate and reset the
oldest-value-still-safe-to-use to one known to remain after truncation.

Per bug reported by Jeff Janes in the course of his tests involving
bug #8673.

While at it, update some comments that hadn't been updated since
multixacts were changed.

Backpatch to 9.3, where persistency of pg_multixact files was
introduced by commit 0ac5ad5134f2.
Allow pushdown of WHERE quals into subqueries with window functions.

We can allow this even without any specific knowledge of the semantics
of the window function, so long as pushed-down quals will either accept
every row in a given window partition, or reject every such row.  Because
window functions act only within a partition, such a case can't result
in changing the window functions' outputs for any surviving row.
Eliminating entire partitions in this way obviously can reduce the cost
of the window-function computations substantially.

The fly in the ointment is that it's hard to be entirely sure whether
this is true for an arbitrary qual condition.  This patch allows pushdown
if (a) the qual references only partitioning columns, and (b) the qual
contains no volatile functions.  We are at risk of incorrect results if
the qual can produce different answers for values that the partitioning
equality operator sees as equal.  While it's not hard to invent cases
for which that can happen, it seems to seldom be a problem in practice,
since no one has complained about a similar assumption that we've had
for many years with respect to DISTINCT.  The potential performance
gains seem to be worth the risk.

David Rowley, reviewed by Vik Fearing; some credit is due also to
Thomas Mayer who did considerable preliminary investigation.
Remove Alpha and Tru64 support.

Support for running postgres on Alpha hasn't been tested for a long
while. Due to Alpha's uniquely lax cache coherency model it's a hard
to develop for platform (especially blindly!) and thought to be
unlikely to currently work correctly.

As Alpha is the only supported architecture for Tru64 drop support for
it as well. Tru64's support has ended 2012 and it has been in
maintenance-only mode for much longer.

Also remove stray references to __ksr__ and ultrix defines.
Add cluster_name GUC which is included in process titles if set.

When running several postgres clusters on one OS instance it's often
inconveniently hard to identify which "postgres" process belongs to
which postgres instance.

Add the cluster_name GUC, whose value will be included as part of the
process titles if set. With that processes can more easily identified
using tools like 'ps'.

To avoid problems with encoding mismatches between postgresql.conf,
consoles, and individual databases replace non-ASCII chars in the name
with question marks. The length is limited to NAMEDATALEN to make it
less likely to truncate important information at the end of the
status.

Thomas Munro, with some adjustments by me and review by a host of people.
Remove use_json_as_text options from json_to_record/json_populate_record.

The "false" case was really quite useless since all it did was to throw
an error; a definition not helped in the least by making it the default.
Instead let's just have the "true" case, which emits nested objects and
arrays in JSON syntax.  We might later want to provide the ability to
emit sub-objects in Postgres record or array syntax, but we'd be best off
to drive that off a check of the target field datatype, not a separate
argument.

For the functions newly added in 9.4, we can just remove the flag arguments
outright.  We can't do that for json_populate_record[set], which already
existed in 9.3, but we can ignore the argument and always behave as if it
were "true".  It helps that the flag arguments were optional and not
documented in any useful fashion anyway.
merge master