* tests/gpgscm/init.scm (vm-history-print): New function.
* tests/gpgscm/opdefines.h: New opcodes 'CALLSTACK_POP', 'APPLY_CODE',
and 'VM_HISTORY'.
* tests/gpgscm/scheme-private.h (struct history): New definition.
(struct scheme): New field 'history'.
* tests/gpgscm/scheme.c (gc): Mark objects in the history.
(history_free): New function.
(history_init): Likewise.
(history_mark): Likewise.
(add_mod): New macro.
(sub_mod): Likewise.
(tailstack_clear): New function.
(callstack_pop): Likewise.
(callstack_push): Likewise.
(tailstack_push): Likewise.
(tailstack_flatten): Likewise.
(callstack_flatten): Likewise.
(history_flatten): Likewise.
(opexe_0): New variable 'callsite', keep track of the expression if it
is a call, implement the new opcodes, record function applications in
the history.
(opexe_6): Implement new opcode.
(scheme_init_custom_alloc): Initialize history.
(scheme_deinit): Free history.
* tests/gpgscm/scheme.h (USE_HISTORY): New macro.