pgsql: Added the Skytools extended transaction ID module to contrib as

Log Message:
-----------
Added the Skytools extended transaction ID module to contrib as discussed
on CORE previously.

This module offers transaction ID's containing the original XID and the
transaction epoch as a bigint value to the user level. It also provides
a special txid_snapshot data type that contains an entire transactions
visibility snapshot information, which is useful to determine if a
particular txid was visible to a transaction or not.

The module has been tested by porting Slony-I from using its original
xxid data type.

Jan

Modified Files:
--------------
pgsql/contrib:
Makefile (r1.78 -> r1.79)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile?r1=1.78&r2=1.79)

Added Files:
-----------
pgsql/contrib/txid:
Makefile (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/Makefile?rev=1.1&content-type=text/x-cvsweb-markup)
README.txid (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/README.txid?rev=1.1&content-type=text/x-cvsweb-markup)
txid.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/txid.c?rev=1.1&content-type=text/x-cvsweb-markup)
txid.sql.in (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/txid.sql.in?rev=1.1&content-type=text/x-cvsweb-markup)
uninstall_txid.sql (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/uninstall_txid.sql?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/contrib/txid/expected:
txid.out (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/expected/txid.out?rev=1.1&content-type=text/x-cvsweb-markup)
pgsql/contrib/txid/sql:
txid.sql (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/txid/sql/txid.sql?rev=1.1&content-type=text/x-cvsweb-markup)