[FIX] component: strict check of deep argument truth value

With this commit, we make sure that the `render` method was explicitely
called with the deep === true argument, instead of assuming that it is a
boolean.  This prevents errors when some unrelated value is given to the
render method. This could happen in some cases, such as

useBus(someBus, 'someevent', this.render)

In that case, the `useBus` code would simply call the this.render with a
customevent, which would be considered truthy before, and not anymore

doc/reference/component.md

@@ -76,7 +76,8 @@ The `Component` class has a very small API.
 
   By default, the render initiated by this method will stop at each child
   component if their props are (shallow) equal. To force a render to update
-  all child components, one can use the optional `deep` argument.
+  all child components, one can use the optional `deep` argument. Note that the
+  value of the `deep` argument needs to be a boolean, not a truthy value.
 
 ## Static Properties