made get_constant_value look through scalar casts

theano/tensor/basic.py

@@ -500,8 +500,9 @@ def get_constant_value(v):
         # Don't act as the constant_folding optimization here as this
         # fct is used too early in the optimization phase.  This would
         # mess with the stabilization optimization.
-        if isinstance(v.owner.op, Elemwise) and isinstance(
-            v.owner.op.scalar_op, scal.Cast):
+        if (isinstance(v.owner.op, Elemwise) and isinstance(
+            v.owner.op.scalar_op, scal.Cast)) or \
+            isinstance(v.owner.op, scal.Cast):
             const = get_constant_value(v.owner.inputs[0])
             ret = [[None]]
             v.owner.op.perform(v.owner, [const], ret)