session persistent data for plperl

The attached tiny patch (not intended for application yet) provides a
space for plperl functions to create and share session persistent data,
which I should think would increase the utility of plperl. Essentially
it creates a hash called %session_globals which it then injects into the
safe container where plperl functions live.

Comments are welcome - this is just a proof of concept. If this seems
good to people, I will try to use a similar mechanism to "register"
plperl functions so they can call each other.

cheers

andrew

(stupid) example use (using dollar quoting in psql ;-) ):

andrew=# create function perlfunc() returns text language plperl as $$
andrew$# if (!exists $session_globals{x}) { $session_globals{x} =
'abcxyz'; }
andrew$# return $session_globals{x}++;
andrew$# $$;
CREATE FUNCTION
andrew=# select perlfunc();
perlfunc
----------
abcxyz
(1 row)

andrew=# select perlfunc();
perlfunc
----------
abcxza
(1 row)

andrew=# create function perlfunc2() returns text language plperl as $$
andrew$# if (!exists $session_globals{x}) { $session_globals{x} =
'abcxyz'; }
andrew$# $session_globals{x} = reverse $session_globals{x};
andrew$# return $session_globals{x}++;
andrew$# $$;
CREATE FUNCTION
andrew=# select perlfunc2();
perlfunc2
-----------
bzxcba
(1 row)

andrew=# select perlfunc2();
perlfunc2
-----------
bbcxzb
(1 row)

andrew=# select perlfunc();
perlfunc
----------
bbcxzc
(1 row)