gpg: Add option --use-ocb-sym
* g10/gpg.c (oUseOCBSym): New. (opts): Add --use-ocb-sym. (main): Set it. * g10/options.h (opt): Add field use_ocb_sym. * g10/encrypt.c (encrypt_symmetric): Take care of the new option. (use_aead): Ditto.
In contrast to --force-ocb this new option is dedicated for symmetric
encryption and can thus be put into a configuration file without
disturbing the preference system.