Tag Alloc and Assert for float16 since they will work.

theano/tensor/basic.py

@@ -2774,6 +2774,7 @@ class Alloc(gof.Op):
     are lifted, the first argument to fill can often be pruned from the graph.
 
     """
+    _f16_ok = True
     __props__ = ()
 
     def validate_shape(self, shape):

theano/tensor/opt.py

@@ -2238,7 +2238,7 @@ class Assert(T.Op):
     >>> func = theano.function([x], assert_op(x, x.size<2))
 
     """
-
+    _f16_ok = True
     __props__ = ('msg',)
     view_map = {0: [0]}