Update pynac to version 0.2.5

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/13316">trac #13316</a>.

A new version of pynac was recently released and fixes some bugs.
Let's include that new version in Sage.

Try the spkg at:
http://perso.telecom-paristech.fr/~flori/sage/pynac-0.2.5.spkg

Ticket <a href="http://trac.sagemath.org/sage_trac/ticket/13107">trac #13107</a> in dependencies includes the related doctests.

Reported by: jpflori

Component: symbolics

CC: burcin,, jpflori,, kcrisman

Report Upstream: N/A

Authors: Jean-Pierre Flori

Dependencies: <a href="http://trac.sagemath.org/sage_trac/ticket/13107">trac #13107</a>

Work issues: 

Reviewers: Burcin Erocal

Merged in: sage-5.4.beta2

Attachments: <ol></ol>