* tests/gpgscm/opdefines.h: Use 0 instead of NULL.
* tests/gpgscm/scheme.c (op_code_info): Use char arrays instead of
pointers, make arity parameters smaller.
(INF_ARG): Adapt.
(_OP_DEF): Likewise.
(dispatch_table): Likewise.
(procname): Likewise.
(Eval_cycle): Likewise.
(scheme_init_custom_alloc): Likewise.