Added activeOrders method to support the new ActiveOrders API method.  Unlike orderList, activeOrders will not fail with an exception when there are no orders; instead, an empty dict will be returned.
Added a warning to orderList as it will be removed from the server on December 1, 2013.
Updated compute-account-value.py sample to use activeOrders instead of orderList.
compute-account-value.py now explicitly says there are no orders instead of failing with an exception.
Fix PEP8/pylint complaints.