pgsql: Implement current_query(), that shows the currently executing

Log Message:
-----------
Implement current_query(), that shows the currently executing query.
At the same time remove dblink/dblink_current_query() as it is no longer
necessary
*BACKWARD COMPATIBILITY ISSUE* for dblink

Tomas Doran

Modified Files:
--------------
    pgsql/contrib/dblink:
        dblink.c (r1.71 -> r1.72)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/dblink.c?r1=1.71&r2=1.72)
        dblink.h (r1.19 -> r1.20)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/dblink.h?r1=1.19&r2=1.20)
        dblink.sql.in (r1.14 -> r1.15)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/dblink.sql.in?r1=1.14&r2=1.15)
        uninstall_dblink.sql (r1.5 -> r1.6)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/uninstall_dblink.sql?r1=1.5&r2=1.6)
    pgsql/contrib/dblink/expected:
        dblink.out (r1.21 -> r1.22)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/expected/dblink.out?r1=1.21&r2=1.22)
    pgsql/contrib/dblink/sql:
        dblink.sql (r1.18 -> r1.19)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/dblink/sql/dblink.sql?r1=1.18&r2=1.19)
    pgsql/doc/src/sgml:
        dblink.sgml (r1.3 -> r1.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/dblink.sgml?r1=1.3&r2=1.4)
        func.sgml (r1.425 -> r1.426)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.425&r2=1.426)
    pgsql/src/backend/utils/adt:
        misc.c (r1.58 -> r1.59)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/misc.c?r1=1.58&r2=1.59)
    pgsql/src/include/catalog:
        pg_proc.h (r1.485 -> r1.486)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.485&r2=1.486)
    pgsql/src/include/utils:
        builtins.h (r1.310 -> r1.311)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.310&r2=1.311)