avoid traps in repl except when evaluating the expression

avoid traps in repl except when evaluating the expression

* module/system/vm/trap-state.scm (with-default-trap-handler): Don't
  enable traps if we are setting a handler of #f.

* module/system/repl/error-handling.scm (call-with-error-handling): Add
  #:trap-handler arg.

* module/system/repl/repl.scm (run-repl): Only have traps enabled while
  running the thunk. Otherwise we trace on procedures called as part of
  the repl.