Assert that we don't have more than one output until we fix the problem of inplace overwriting.

theano/sandbox/gpuarray/elemwise.py

@@ -185,6 +185,7 @@ class GpuElemwise(HideC, Elemwise):
         p = 0
         for n, o in enumerate(node.outputs):
             if n in self.inplace_pattern:
+                assert(len(node.outputs) == 1);
                 res += "\nargs[%(n)s].flags |= GE_WRITE;\n" % dict(n=self.inplace_pattern[n])
             else:
                 nn = len(inps) + p