pgsql: Move dbsize functions into the backend.

Log Message:
-----------
Move dbsize functions into the backend. New functions:

pg_tablespace_size
pg_database_size
pg_relation_size
pg_complete_relation_size
pg_size_pretty

Remove /contrib/dbsize.

Dave Page

Modified Files:
--------------
pgsql/contrib:
Makefile (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/Makefile.diff?r1=1.57&r2=1.58)
pgsql/doc/src/sgml:
diskusage.sgml (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/diskusage.sgml.diff?r1=1.14&r2=1.15)
func.sgml (r1.272 -> r1.273)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.272&r2=1.273)
pgsql/src/backend/utils/adt:
Makefile (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/Makefile.diff?r1=1.57&r2=1.58)
pgsql/src/include/catalog:
pg_proc.h (r1.378 -> r1.379)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.378&r2=1.379)
pgsql/src/include/utils:
builtins.h (r1.261 -> r1.262)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h.diff?r1=1.261&r2=1.262)

Added Files:
-----------
pgsql/src/backend/utils/adt:
dbsize.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/dbsize.c?rev=1.1&content-type=text/x-cvsweb-markup)

Removed Files:
-------------
pgsql/contrib/dbsize:
Makefile
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dbsize/Makefile)
README.dbsize
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dbsize/README.dbsize)
dbsize.c
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dbsize/dbsize.c)
dbsize.sql.in
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/dbsize/dbsize.sql.in)