pgsql: Rewrite rint() to enable removal of copyright mention; patch

Log Message:
-----------
Rewrite rint() to enable removal of copyright mention; patch from
Nathan Wagner

Function is simpler too.

Modified Files:
--------------
pgsql/src/port:
rint.c (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/rint.c?r1=1.2&r2=1.3)