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)