pgsql: Let's try forcing errno to zero before issuing fsync.

Log Message:
-----------
Let's try forcing errno to zero before issuing fsync. The current buildfarm
results claiming EBADF seem improbable enough that I'm not convinced fsync
is really returning that --- could it be failing to set errno at all?

Modified Files:
--------------
pgsql/src/port:
copydir.c (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/copydir.c?r1=1.30&r2=1.31)