bug#56682: Fix the long lines font locking related slowdowns

[Gregory Heytings]

> Just before the Devanagari portion of the file, there's the Hebrew 
> portion, starting around buffer position 3243400.  If you go there and 
> try the same navigation commands that were slow with Arabic, are they as 
> slow with Hebrew (which is also a right-to-left script, but doesn't use 
> character compositions nearly as heavily as Arabic)?  Here it looks like 
> Hebrew is noticeably faster, as fast as Devanagari.

Sorry, I hadn't seen this post before replying to the previous one. 
Indeed, as I said in my previous reply navigation commands in Hebrew texts 
are much faster than in Arabic texts.