Lang???.gf: exclude Documentation from present mode

The Documentation module is excluded from present mode in abstract/Lang.gf,
so it needs to be excluded in the corresponding concrete syntaxes too
to avoid problems.

src/french/LangFre.gf

@@ -3,7 +3,7 @@
 concrete LangFre of Lang = 
   GrammarFre,
   LexiconFre
-  ,DocumentationFre
+  ,DocumentationFre --# notpresent
   ,ConstructionFre
   ** {