Support the not anymore patented IDEA cipher algorithm.
* cipher/idea.c: New. Take from Libgcrypt master and adjust for direct use in GnuPG. * cipher/idea-stub.c: Remove. * cipher/Makefile.am: Add idea.c and remove idea-stub.c rules. * configure.ac: Remove idea-stub code. * g10/gpg.c (check_permissions): Remove code path for ITEM==2. (main): Make --load-extension a dummy option. * g10/keygen.c (keygen_set_std_prefs): Include IDEA only in PGP2 compatibility mode. * g10/misc.c (idea_cipher_warn): Remove. Also remove all callers. * g10/seckey-cert.c (do_check): Remove emitting of STATUS_RSA_OR_IDEA. * g10/status.c (get_status_string): Remove STATUS_RSA_OR_IDEA. * g10/status.h (STATUS_RSA_OR_IDEA): Remove.
To keep the number of actually used algorithms low, we support IDEA
only in a basically read-only way (unless --pgp2 is used during key
generation). It does not make sense to suggest the use of this old 64
bit blocksize algorithm. However, there is old data available where
it might be helpful to have IDEA available.