This patch started as an adaptation of the fix described at http://stackoverflow.com/questions/5738173/
Based on a suggestion by Patrick on the grappelli Google group, it has
been further modified so that it should work with any tinyMCE mode
setting, not just "textfields". See also
https://groups.google.com/forum/#!topic/django-grappelli/hU_e2qmN_uc