avidemux: don't require 'find' explicitly
vmalloc: download_strategy is loaded by formula
openssl: create a cert.pem file from keychain certs

Closes #21065.
graphicsmagick: use optional dep for ghostscript
fceux: remove failing inreplace

Both replaces currently fail. However it built fine without them and
linked to the correct libraries, at least under superenv. If it breaks
under stdenv someone will have to patch it, but nobody has complained so
far.
cogl: fix deps
Make the use of paths to packages proxied through X11 consistent