FIXED: setup_call_cleanup/4: Avoid superfluous calling of the cleanup
handler because FR_WATCHED is set by the debugger or frame inspection.
Matt Lilley.
Avoid runtime lookup of user:event_hook/1.
Cleanup calling of (debugger) event hook.  Avoid a function call for the
common case that the hook is not installed and centralise dependency on
whether or not the debugger is configured.