Remove the dict constraint in ForwardRef._eval_type (#252)

This improves compatibility with Pyston, which doesn't use a dict for globals.
I'm not sure if there is a better solution, but just removing the check seems ok:
eval() will still do type checking, and though the error messages won't be
as nice I think it's ok because this is all internal (the locals/globals seem
to come from f_locals/f_globals).

Author: kmod

python2/typing.py

@@ -155,12 +155,6 @@ def __new__(cls, arg):
         return self
 
     def _eval_type(self, globalns, localns):
-        if not isinstance(localns, dict):
-            raise TypeError('ForwardRef localns must be a dict -- got %r' %
-                            (localns,))
-        if not isinstance(globalns, dict):
-            raise TypeError('ForwardRef globalns must be a dict -- got %r' %
-                            (globalns,))
         if not self.__forward_evaluated__:
             if globalns is None and localns is None:
                 globalns = localns = {}

src/typing.py

@@ -160,12 +160,6 @@ def __new__(cls, arg):
         return self
 
     def _eval_type(self, globalns, localns):
-        if not isinstance(localns, dict):
-            raise TypeError('ForwardRef localns must be a dict -- got %r' %
-                            (localns,))
-        if not isinstance(globalns, dict):
-            raise TypeError('ForwardRef globalns must be a dict -- got %r' %
-                            (globalns,))
         if not self.__forward_evaluated__:
             if globalns is None and localns is None:
                 globalns = localns = {}