Change IPython widget warning to get rid of filenames and line numbers

We do this to not confuse the interactive user

IPython/html/widgets/__init__.py

@@ -1,29 +1,32 b''
 from .widget import Widget, DOMWidget, CallbackDispatcher, register
 
 from .widget_bool import Checkbox, ToggleButton
 from .widget_button import Button
 from .widget_box import Box, Popup, FlexBox, HBox, VBox
 from .widget_float import FloatText, BoundedFloatText, FloatSlider, FloatProgress, FloatRangeSlider
 from .widget_image import Image
 from .widget_int import IntText, BoundedIntText, IntSlider, IntProgress, IntRangeSlider
 from .widget_output import Output
 from .widget_selection import RadioButtons, ToggleButtons, Dropdown, Select
 from .widget_selectioncontainer import Tab, Accordion
 from .widget_string import HTML, Latex, Text, Textarea
 from .interaction import interact, interactive, fixed, interact_manual
 from .widget_link import Link, link, DirectionalLink, dlink
 
 # Deprecated classes
 from .widget_bool import CheckboxWidget, ToggleButtonWidget
 from .widget_button import ButtonWidget
 from .widget_box import ContainerWidget, PopupWidget
 from .widget_float import FloatTextWidget, BoundedFloatTextWidget, FloatSliderWidget, FloatProgressWidget
 from .widget_image import ImageWidget
 from .widget_int import IntTextWidget, BoundedIntTextWidget, IntSliderWidget, IntProgressWidget
 from .widget_selection import RadioButtonsWidget, ToggleButtonsWidget, DropdownWidget, SelectWidget
 from .widget_selectioncontainer import TabWidget, AccordionWidget
 from .widget_string import HTMLWidget, LatexWidget, TextWidget, TextareaWidget
 
-# Warn on import
-from warnings import warn
-warn("IPython widgets are experimental and may change in the future.", FutureWarning, stacklevel=2)
+# we use warn_explicit so we have very brief messages without file or line numbers
+# the concern is that file or line numbers will confuse the interactive user
+from warnings import warn_explicit
+__warningregistry__ = {}
+warn_explicit("IPython widgets are experimental and may change in the future.",
+              FutureWarning, '', 0, registry=__warningregistry__)