Try to use "md5" binary not md5sum if md5sum can't be found.
installerStub now allows BSD Style md5sum to work (don't use - param)
Offer to continue install anyway if MD5 not found in file, or unable to be calculated (no md5sum)
git-svn-id: http://svn.dmdirc.com/trunk@423300569f92-eb28-0410-84fd-f71c24880f
Lotsa changes to the linux installer to make it also run on OpenSolaris (and possibly normal solaris aswell, I don't have gui access to a normal solaris machine from here will try when I go back to uni)