[rand] use sys.maxsize instead of sys.maxint

Python 3 does not have sys.maxint, because int is limitless in Python 3.
On most setups in Python 2, sys.maxsize equals to sys.maxint, so using
sys.maxsize should not be a problem.
[core] nitpick: don't use u'' strings

We use from __future__ import unicode_literals, so the u before the string
is meaningless