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.