[pyramid/security] use cryptographically secure random generator
Based on django source code in case SystemRandom is not available.
According to python documentation:
https://docs.python.org/2/library/random.html
> Warning
> The pseudo-random generators of this module should not be used for security
> purposes. Use os.urandom() or SystemRandom if you require a cryptographically
> secure pseudo-random number generator.
.. _rset_module:
:mod:`cubicweb.rset`
====================
.. automodule:: cubicweb.rset
.. autoclass:: ResultSet
:members: