arabic test sentences

From "Automating the generation and typesetting of Arabic script" by Mansour,
test in §5.4.3:

> The eight sentences were chosen to test these main features:
> - Each letter is correctly generated without compatibility problems with MetaPost
> - Choosing the correct forms of letters (context analysis engine test)
> - Connections between letters (joining problems that require modification in Meta-font files)
> - Kerning