core: Do not leak the override session key to ps(1).
* src/engine-gpg.c (struct engine_gpg): New field override_session_key. (gpg_release): Free that field. (gpg_decrypt): With gnupg 2.1.16 use --override-session-key-fd. * tests/run-decrypt.c (main): Fix setting over the override key.
Note that this works only with gnupg 2.1.16 and later.
- Signed-off-by: Werner Koch <wk@gnupg.org>