pgsql: Make details of the Numeric representation private to numeric.c.

Log Message:
-----------
Make details of the Numeric representation private to numeric.c.

Review by Tom Lane.

Modified Files:
--------------
    pgsql/contrib/btree_gist:
        btree_numeric.c (r1.13 -> r1.14)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/btree_gist/btree_numeric.c?r1=1.13&r2=1.14)
    pgsql/src/backend/utils/adt:
        format_type.c (r1.53 -> r1.54)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/format_type.c?r1=1.53&r2=1.54)
        numeric.c (r1.123 -> r1.124)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/numeric.c?r1=1.123&r2=1.124)
    pgsql/src/include/utils:
        numeric.h (r1.29 -> r1.30)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/numeric.h?r1=1.29&r2=1.30)