Rename 'while' -> 'do_while', at least one step will always be executed.

theano/scan_module/scan_op.py

@@ -316,7 +316,7 @@ class Scan(Op):
         else:
             gpu_str = 'cpu'
         if self.as_while:
-            name = 'while'
+            name = 'do_while'
         else:
             name = 'for'