Revert "BUG: Capital change deltas rely on cash, not portfolio_value" (#1470)

This reverts commit 5b1aa5ec55.

The paradigm is: we're calculating a new capital base for the
performance period. We are therefore using the total
portfolio_value, not just the cash, to calculate the
difference from the specified target as the algorithm
has meaningful holdings.

zipline/algorithm.py

@@ -862,7 +862,8 @@ class TradingAlgorithm(object):
         if capital_change['type'] == 'target':
             target = capital_change['value']
             capital_change_amount = target - \
-                (self.updated_portfolio().cash - portfolio_value_adjustment)
+                (self.updated_portfolio().portfolio_value -
+                 portfolio_value_adjustment)
             self.portfolio_needs_update = True
 
             log.info('Processing capital change to target %s at %s. Capital '