DefinitionSummary: favor last hovered definition

While there's an in-flight definition summary request, and the user
hovers over a new definition, discard the original one in favor of the
newly hovered definition.

src/Code/DefinitionSummaryTooltip.elm

@@ -76,14 +76,28 @@ update config msg model =
  ( { model | activeTooltip = cached }, Cmd.none )
 
  FetchDefinition ref ->
+ let
+ fetchDef =
+ ( { model | activeTooltip = Just ( ref, Loading ) }
+ , fetchDefinition config ref |> HttpApi.perform config.api
+ )
+ in
  case model.activeTooltip of
+ Just ( r, Loading ) ->
+ if Reference.equals ref r then
+ ( model, Cmd.none )
+
+ else
+ -- If we've moved on to hovering over a different
+ -- definition while another was loading, discard the
+ -- original request
+ fetchDef
+
  Just _ ->
  ( model, Cmd.none )
 
  Nothing ->
- ( { model | activeTooltip = Just ( ref, Loading ) }
- , fetchDefinition config ref |> HttpApi.perform config.api
- )
+ fetchDef
 
  HideTooltip _ ->
  ( { model | activeTooltip = Nothing }, Cmd.none )