Tweaked IntEntry behavior

Changed behavior of IntEntry to stop it from continously selecting all
text as long as the mouse is over the input box.  It appears that
something continues to send kMouseEnterMessage messages while use is
typing, even if the mouse is still.  This caused the IntEntry select-all
multiple times and as the user typed would replace what they had already
written.

Note: The base Entry widget already does a select-all on mouse enter, so the desired auto-select behavior is retained.