buildsystem: add 'post_unpack'

this is built-in PKG_DIR/rename replacement
hd-idle: remove 'rename' script
vdr-control: remove 'rename' script
vdr-iptv: remove 'rename' script
vdr-live: remove 'rename' script
vdr-wirbelscan: remove 'rename' script
vdr-wirbelscancontrol: remove 'rename' script
buildsystem: unpack on any package.mk change
buildsystem: always clean up $INSTALL / .$TARGET_NAME on rebuild
update TODO
buildsystem: fix c/p mistake in ef272b04