rsync: add upstream security fix for CVE-2017-16548

rsync: add upstream security fix for CVE-2017-16548

The receive_xattr function in xattrs.c in rsync 3.1.2 and 3.1.3-development
does not check for a trailing '\0' character in an xattr name, which allows
remote attackers to cause a denial of service (heap-based buffer over-read
and application crash) or possibly have unspecified other impact by sending
crafted data to the daemon.

For more details, see:
https://bugzilla.samba.org/show_bug.cgi?id=13112

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>