Detection and reporting of unrar binary version, and rar version of rar files

Detection and reporting of unrar binary version, and rar version of rar files, as discussed on https://forums.sabnzbd.org/viewtopic.php?f=4&t=17490

Example output in sabnzbd.log:

2014-05-07 21:40:31,845::INFO::[SABnzbd:484] unrar binary version is: UNRAR 5.00 beta 8 freeware
...
2014-05-07 22:06:32,256::DEBUG::[newsunpack:599] Type of rar file is Rar4 or lower

Some exception handling may be needed. It would be a shame if SABnzbd simply crashed on a bad RAR program.