scan/scan_op: Convert known_grads to OrderedDict

This was probably causing a different order of operation during gradient computation in scan for each run. With this fix I'm able to finally reproduce results on my RNN system.

scan/scan_op: Convert known_grads to OrderedDict
8769382f · Ozan Çağlayan · 5f0cf1c3 · 8769382f
--- a/theano/scan_module/scan_op.py
+++ b/theano/scan_module/scan_op.py
@@ -2024,7 +2024,7 @@ class Scan(PureOp):
            # it will be the sum of the external gradient signal and the
            # gradient obtained by propagating Y's external gradient signal
            # to X.
-            known_grads = dict([(k.copy(), v) for (k, v) in known_grads.items()])
+            known_grads = OrderedDict([(k.copy(), v) for (k, v) in known_grads.items()])

            grads = gradient.grad(
                        cost=None,
@@ -2094,7 +2094,7 @@ class Scan(PureOp):
            dC_dXts.append(dC_dXt)


-        known_grads = {}
+        known_grads = OrderedDict()
        dc_dxts_idx = 0
        for i in range(len(diff_outputs)):
            if i < idx_nitsot_start or i >= idx_nitsot_end: