Before this change the GIF wasn't sent at all when the PHP settings
indicate that sending of the GIF needs to be deferred and it was sent
when the debug output was on.

  - removed some dead/unused code
  - fixed phpdoc
  - added typing on methods

the function always returned true, even if no action was taken. This
resulted in no further indexer tasks being run.

fixes the problem with missing innerText in Firefox (and other browsers)
and corrects shortening in regard to paddings and the use of the
text-overflow attribute

* added more selectors to allow different markup
* added border to make tabs more distinctive, especially in other templates

#2541, alter section highlighting to insert a container into the DOM to hold the elements being highlighted & later remove it

note: we recommend to NOT use H1 elements in the sidebar for semantic
reasons

Replaced it by the old tpl_include_page() and made it more flexible by adding a boolean $propagate parameter.
(It's false by default for backwards compatibility reasons. Should it rather be true? That would probably be what most users want.)