BUG #4660: float functions return -0

The following bug has been logged online:

Bug reference: 4660
Logged by: ITAGAKI Takahiro
Email address: itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp
PostgreSQL version: 8.3.3
Operating system: Fedora 8
Description: float functions return -0
Details:

Float8 versions of trunc(), ceil() and round() could return -0 on some
version of glibc.

We avoid -0 in float8um (unary minus),
but should we add the same codes in those functions?
There is inconsistency compared with numeric version
of funcs and it is a platform-dependent behavior;
0 is returned there.

postgres=# SELECT pg_catalog.trunc((-0.1)::float8);
trunc
-------
-0
(1 row)

postgres=# SELECT pg_catalog.ceil((-0.1)::float8);
ceil
------
-0
(1 row)

postgres=# SELECT pg_catalog.round((-0.1)::float8);
round
-------
-0
(1 row)

postgres=# select version();
version
----------------------------------------------------------------------------
------------------------
PostgreSQL 8.3.3 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 4.1.1
20070105 (Red Hat 4.1.1-51)
(1 row)