Remove a load of identical definitions of set_difference.

Signed-off-by: John Else <john.else@citrix.com>
Remove unused function for handling RHEL3.

This function hasn't been used since Oxford, and we haven't supported
RHEL 3 for a while.

Signed-off-by: John Else <john.else@citrix.com>
Fix typos.

Signed-off-by: John Else <john.else@citrix.com>