Escaping slash in "content_history_options" -> "form_field" for com_contact

The content_type for com_contact has some inconsistent escaping of the slash in "content_history_options" -> "form_field".
Properly escaped the slash looks like this in JSON: "\/" and this escaped JSON string has to be escaped again for MySQL query like this: "\\/".

Tracker:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31937