* tests/gpgscm/scheme-private.h (struct scheme): Make 'vptr' const.
* tests/gpgscm/scheme.c (num_zero): Statically initialize and turn
into constant.
(num_one): Likewise.
(charnames): Change type so that it can be stored in rodata.
(is_ascii_name): Adapt slightly.
(assign_proc): Make argument const char *.
(op_code_info): Make some fields const char *.
(tests): Make const.
(dispatch_table): Make const.  At least it can be made read-only after
relocation.
(Eval_Cycle): Adapt slightly.
(vtbl): Make const.