tests: Implement interpreter shutdown using exceptions.
* tests/gpgscm/ffi.c (ffi_init): Rename 'exit' to '_exit'. * tests/gpgscm/ffi.scm (*interpreter-exit*): New variable. (throw): New function. (exit): New function.
This allows a proper cleanup of resources.
- Signed-off-by: Justus Winter <justus@g10code.com>