wishlist/missing features:

*) handle sign-only keys: dont encrypt to those, don't look at them
	during the listing of keys. try to use encrypt-only keys first

*) maybe support s/mime as well, for example using openssl's smime helper?

*) maybe make kuvert_mta_wrapper log into kuvert's logfile, too?

*) kuvert_mta_wrapper should honor the MTA option if possible

*) add warning for duplicate keys 

