[vdr] change make install to be really useful

Hi there!

I now switched the ebuilds to use make install. But for that to work I needed to modify the Makefile.

install-i18n.diff Lets install target call install-i18n target.

makefile-destdir.diff: It add variable DESTDIR to makefile to install under $(DESTDIR) instead of / It also adds variable CONFDIR (by default identical to $(VIDEODIR)) to be able to set it to different value. Additionally it installs svdrpsend.pl

makefile-install-header.diff: It adds an install-header target which is also called by target install. This installs the header files and Make.config to $(HEADERDIR) (should that be changed to INCDIR ?) to be able to compile plugins against the installed vdr without the need to keep vdr sources.

Matthias