Improve 'clean-ps' and 'clean-pdf' targets (as well as 'wipe-' ones)

Re-write 'clean-ps', 'clean-pdf', 'wipe-ps' and 'wipe-pdf' targets
to be only dependent on $(ext) and $(extsec) variables.
Now the 'wipe-' targets invoked for the derivative output format
also remove the primary output format files