breakpoints from recursive prompts work

breakpoints from recursive prompts work

* module/system/vm/traps.scm (new-disabled-trap): Don't manipulate the
  VM trace level in the enable and disable handlers. Unfortunately, this
  makes traps not work unless you enable hooks, but given that
  vm_dispatch_hook has to set trace-level to 0, there needs to be an
  object with a broader view of what traps are enabled. That object is
  the hook state.

* module/system/vm/trap-state.scm (trap-state->trace-level): New
  procedure.
  (with-default-trap-handler): Add an optional trap-state argument. Now
  makes sure that the vm-trace-level is set appropriately during the
  execution of the thunk, allowing for breakpoints from recursive
  prompts.