tests/gpgscm: Expose function to open streams as Scheme ports.
* tests/gpgscm/scheme.c (vtbl): Add 'port_from_file' to the vtable. * tests/gpgscm/scheme.h (struct scheme_interface): New field 'mk_port_from_file'.
- Signed-off-by: Justus Winter <justus@g10code.com>