sh-script.el : don't colorize $(( 4 << 2 )) as here-document

[Thomas Gambier <thomas_gambier@sdesigns.eu>]

Hello,

when I'm writing something like this in bash script value=$(( 4 << 2 )), 
Emacs keep thinking it's the beginning of here-document and will 
colorize in yellow all the code below this expression.

I've seen that a bug in sh-script.el was corrected so that << between "" 
won't be interpreted as a beginning of here-document 
(http://lists.gnu.org/archive/html/help-gnu-emacs/2003-06/msg00158.html). 
Is there any solution to don't consider also << between $(( )) ? I 
looked into sh-script.el to try to correct it myself but I'm not very at 
ease with lisp and regular expression and I didn't find what to change. 
That's why I ask help here. If it's not possible, I will disable the 
feature as explained in the previous link.

Best regards.

-- 
Thomas Gambier.