* Implement posix-sema.c

* Add gpgme_mime_xxx to make handling of MIME/PGP easier

* Allow to use GTK's main loop instead of the select stuff in
  wait.c

* add locking to the key cache?

* Should --delete silently delete secret keys or is there a need for
  another flag or a callback?

* There is no status response if we have no usable recipients - must
  add one to gpg so that gpgme_encrypt does return with an error.