search builder: unable to search activity details

we don't have a clause to escape fields of type "Text" in CRM_Utils_Type::escape() which causes a fatal. simply adding the case to the existing String/Memo case doesn't work because the query is built without wrapping the value in quotes (e.g. ( LOWER(civicrm_activity.details) LIKE searchterm ) )

we could wrap the term in quotes in the escape function case, but I think we want to look higher up the tree to figure out why it's not treating Text type fields as a string when building the query