How to get the connected forms of Syriac letters?

[Fabian Rieger <cjkv@freenet.de>]

Is there a method to make Emacs show the connected (initial, medial, 
final) forms of Syriac letters?
I'm using the Unicode-OpenType Meltho fonts, in Iceweasel/Firefox this 
works fine, but Emacs gives nothing but the isolated forms.
    The shaping of Arabic seems to work fine (I can't read it, but the 
letters change to isolated forms and back when a space is added or 
deleted inside a copyed word).
    My fonts:

       (set-default-font "DejaVu Sans Mono 20")
       (set-fontset-font "fontset-default" 'syriac
                 "Serto Jerusalem 30")
       (set-fontset-font "fontset-default" 'arabic
                 "Scheherazade 24")

I tried with Debian Wheezy + Emacs 24.4.50.1 (from londo.ganneff.de) & 
25.0.50.1 built with configure option --with-m17n-flt 
(/usr/share/m17n/SYRC-OTF.flt looks promising but doesn't seem to help) 
following
    www.emacswiki.org/emacs-fr/EmacsSnapshotAndDebian
The problem already was there with win2k & Emacs 24.3 a year ago ...

Thanks

Fabian