Bug 17352: synchronize the file before renaming

Bug 17352: synchronize the file before renaming

Dbus is doing atomic file updates by copying them, changing
the copy, and re-naming them. However, it does not synchronize
the file before re-naming, which results in corruption in
case of unclean reboots. The reason for this is that file-systems
have write-back cache and they postpone writing data to the media.

This patch adds the missed fsync() for the Unix part. I do
not have windows so cannot provide a windows port fix.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Colin Walters <walters@verbum.org>