Withdraw PL/Proxy from commitfest

In the previous discussion there was mentioned that Postgres should
move to the SQL-MED direction in remote connection handling.

SQL-MED specifies that connections should have names and referenced
everywhere using names. PL/Proxy currently does not conform to that
standard - it uses connection strings directly. Although it could
made work with SQL-MED backend, it would look ugly.

So I'd like to withdraw PL/Proxy from commitfest and rework it's
connection handling scheme to be also name->connstr based. Idea will
be that it will have user-definable connection handling backend,
which operates on named connections. And in the future we can
plug in a backend that reuses connection info from builtin SQL-MED store.

Although the current connection handling works and is secure it has
a deficiency that it's bit hard to hide the password that is used
for connecting. User can either play with table/function permissions
and SECURITY DEFINER functions but that's complex. Or he can put
passwords into .pgpass - this is easy and secure but has the problem
that the file is not manageable from inside database.

So PL/Proxy needs new SQL-MED based scheme that fixes it. When this
is ready we can re-discuss the builtin vs. PL-based remote functions.
As I don't plan to work on it near-term there is no point polluting
the commitfest page with it.

[ There was a attempt to paint the .pgpass based password handling
insecure because dblink makes the file world-readable. I still
fail to see how this any way points to flaws of the scheme... ]

--
marko