connect a few more wires to promptenstein

connect a few more wires to promptenstein

* libguile/tags.h (scm_tc7_prompt): Allocate a tc7 for prompt objects.

* libguile/control.h (SCM_F_PROMPT_INLINE, SCM_F_PROMPT_ESCAPE)
  (SCM_PROMPT_P, SCM_PROMPT_FLAGS, SCM_PROMPT_INLINE_P)
  (SCM_PROMPT_ESCAPE_P, SCM_PROMPT_TAG, SCM_PROMPT_REGISTERS)
  (SCM_PROMPT_DYNENV, SCM_PROMPT_HANDLER)
  (SCM_PROMPT_PRE_UNWIND_HANDLER, SCM_PROMPT_SETJMP)
  (struct scm_prompt_registers):
* libguile/control.c (scm_c_make_prompt): Flesh out a simple prompts
  implementation.

* libguile/vm-i-system.c (prompt): Wire up the implementation.
* libguile/vm.c: Add a needed #include.