Makefile again adapted to vdr-1.7.36

Hi,

with vdr-1.7.36, the plugin Makefile has been again, modified. Let's hope this is the last change now (DESTDIR moved in the installing targets is quite a change for some distros like Gentoo which have to adapt to one final variant). The current Makefile may still work for you, but if this whole Makefile storm has settled, actually the very last format agreed upon by Klaus and Copperhead should be used consistently by all Plugins which claim they have switched to the "new" Makefile. So please adapt, I think it should work for you, too...

Cheers... L.