* mes.c (r0, r1, r2, r3, stack): New globals.
(gc_loop): Handle MACRO and SCM.
(gc_copy): Handle FUNCTION, allow for pre-allocated SCM and SYMBOL.
(assq): Flag any BROKEN_HEARTs.
(vm_call): New function. Enables moving C stack to GC stack.
(evlis_env, apply_env, eval_env, expand_macro_env, begin_env,
if_env): Use vm_call-indirection.
(call_lambda): New function.
(vm_apply_env): Rename from apply_env. Remove parameters, instead
use r1, r2 and r0.
(vm_evlis_env, vm_eval_env, vm_expand_macro_env, vm_begin_env,
vm_if_env): Likewise.
(acons): New function.
(mes_environment) [!MES_FULL, MES_MINI]: Add cpp switches to create minimally
filled environment, for debugging.
(main): Print free value at exit.
* define.c (define_env): Use vm_call-indirection.
(vm_define_env): Rename from define_env.
* quasiquote.c (eval_quasiquote): Use vm_call-indirection.
(vm_eval_quasiquote): Rename from eval_quasiquote.
* tests/gc-2.test: New test.
tests/gc-2a.test: New test.
tests/gc-3.test: New test.
