rsnapshot: add rsnapshot backup utility

rsnapshot: add rsnapshot backup utility

this adds the rsnapshot backup utility to the packages feed.

To be compatible with busybox logger, I had to patch rsnapshot to don't
pass -i to logger. This package was also proposed in Ticket #11371, but
in a wrong categorie, without this patch, without most of the dependencies
and without the conffiles line to save rsnapshot.conf over sysupgrade.

[florian: fix whitespaces and clean up configure args]

Signed-off-by: Stefan Hellermann <stefan@the2masters.de>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
SVN-Revision: 34508