there are two contrib blocks that uses the treeview YUI component
while patching them to work with hebrew and RTL in general...

i had to add an image file to treeview YUI component that is horizontally mirrored to support RTL
icons visual display when those Blocks are used in an RTL course.

currently, there are two ways to workaround/fix/patch this issue.
1. add a new (horizontally mirrored) gif file the the "assets" folder inside treeview YUI component
2. add the needed file to the local folder of the Block component that uses the YUI treeview
and have the CSS file use the correct gif by using styles.php file and not styles.css

i choose the first option when i fixed the "dir_tree" contrib block and the "yui_course_menu" contrib block
since i thought it is going to be fix (in the future) by YAHOO adding the rtl support upstream.
(please correct me if i am wrong)

dir_tree >> http://moodle.org/mod/data/view.php?rid=1897&page=515
yui_course_menu >> http://moodle.org/mod/data/view.php?d=13&rid=915

i am attaching the horizontally mirrored gif.
it should go into "moodle/lib/yui/treeview/assets"