gpg: New option --require-compliance.

* g10/options.h (opt): Add field flags.require_compliance.
* g10/gpg.c (oRequireCompliance): New.
(opts): Add --require-compliance.
(main): Set option.
* g10/mainproc.c (proc_encrypted): Emit error if non de-vs compliant.
(check_sig_and_print): Ditto.
* g10/encrypt.c (encrypt_crypt): Ditto.
--

Note that in the --encrypt and --verify cased other checks may kick in
earlier than this new --require-compliance controlled one.

g10/options.h

@@ -269,6 +269,9 @@ struct
     /* The next flag is set internally iff IMPORT_CLEAN has
      * been set by the user and is not the default value.  */
     unsigned int expl_import_clean:1;
+    /* Fail if an operation can't be done in the requested compliance
+     * mode.  */
+    unsigned int require_compliance:1;
   } flags;
 
   /* Linked list of ways to find a key if the key isn't on the local