Bugfixes

Changes:

- Initialize `old_globals` after unpickling global variables
- Use `int_to_Integer` on statements

Fixes [issue 3310](https://code.google.com/p/sympy/issues/detail?id=3310) and [issue 3357](https://code.google.com/p/sympy/issues/detail?id=3357).

Deployed at http://68.sympy-live-tests.appspot.com/

Example for issue 3310: http://68.sympy-live-tests.appspot.com/?evaluate=1%2F3%0A%23--%0Ax**(1%2F5)%0A%23--%0A

Example for issue 3357: http://68.sympy-live-tests.appspot.com/?evaluate=variable%20%3D%2013%0A%23--%0Adef%20test()%3A%20print%20variable%0A%23--%0Atest()%0A%23--%0A