Detect busybox logger and change logger cmdline

The busybox logger command (used on embedded systems and such) does not
support the -i option and die squaking if it's used. If the logger
configured is a symlink to busybox, the -i option must not be used.
rsnapshot-diff: Fixed removed files reported as addition (+ mark)

Fix an obvious copy/paste mistake in rsnapshot-diff.pl introduced
by 00e2f5085bd476ab867595d0ecbbed71264e9b5f
Fixed pod2man location.

Uses the pod2man present in the user path. Especially usefull if the
user has perl & pod2man installed in /usr/local/