update to Pynac 0.2.4

[burcin]

There is a new Pynac release which contains fixes to:

• #11155: abs(pi+I) -> pi + I (upstream from Alexei Sheplyakov)
• #11423: atan2(0,0) should be undefined (by Volker Braun)
• #11919: pickling of user defined symbolic functions without custom methods
• #12303: beta should remain symbolic for exact input
• a fix to use Python for comparing Python objects wrapped in numerics (by Jean-Pierre Flori
• complete rewrite of code handling various types of infinity (by Volker Braun)

Following the comments ​this thread on sage-devel, the release is available as a tarball:

​http://sage.math.washington.edu/home/burcin/pynac/pynac-0.2.4.tar.bz2

Patches attached to this ticket need to be applied to the Sage library to update the Pynac interface.