MAINT: Removed unnecessary floating point checks in slippage

Cleaned up some other expressions in slippage as well

Fixes #277

zipline/finance/slippage.py

@@ -24,7 +24,6 @@ from functools import partial
 from six import with_metaclass
 
 from zipline.protocol import DATASOURCE_TYPE
-import zipline.utils.math_utils as zp_math
 
 SELL = 1 << 0
 BUY = 1 << 1
@@ -98,14 +97,10 @@ def transact_stub(slippage, commission, event, open_orders):
     slippage and commission models can be enclosed.
     """
     for order, transaction in slippage(event, open_orders):
-        if (
-            transaction
-            and not
-            zp_math.tolerant_equals(transaction.amount, 0)
-        ):
+        if transaction and transaction.amount != 0:
             direction = math.copysign(1, transaction.amount)
             per_share, total_commission = commission.calculate(transaction)
-            transaction.price = transaction.price + (per_share * direction)
+            transaction.price += per_share * direction
             transaction.commission = total_commission
         yield order, transaction
 
@@ -171,7 +166,7 @@ class SlippageModel(with_metaclass(abc.ABCMeta)):
 
         for order in current_orders:
 
-            if zp_math.tolerant_equals(order.open_amount, 0):
+            if order.open_amount == 0:
                 continue
 
             order.check_triggers(event)
@@ -231,7 +226,7 @@ class VolumeShareSlippage(SlippageModel):
         volume_share = min(total_volume / event.volume,
                            self.volume_limit)
 
-        simulated_impact = (volume_share) ** 2 \
+        simulated_impact = volume_share ** 2 \
             * math.copysign(self.price_impact, order.direction) \
             * event.price