Update PolyBoRi to release 0.8.1

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/12655">trac #12655</a>.

!PolyBoRi's next minor release is out now.
There were no changes of the interface between !PolyBoRi 0.8.0 and 0.8.1, so we just have to update the sources from here:

https://sourceforge.net/projects/polybori/files/polybori/0.8.1

=== Current spkg ===
 * **Install** http://boxen.math.washington.edu/home/dreyer/spkg/polybori-0.8.1.p1.spkg

This also fixes building with GCC-4.7.0, see <a href="http://trac.sagemath.org/sage_trac/ticket/12751">trac #12751</a> for the GCC-4.7.0 metaticket.

Reported by: AlexanderDreyer

Component: packages

CC: PolyBoRi,malb,burcin

Report Upstream: None of the above - read trac for reasoning.

Authors: Alexander Dreyer

Dependencies: <a href="http://trac.sagemath.org/sage_trac/ticket/12656">trac #12656</a>, <a href="http://trac.sagemath.org/sage_trac/ticket/12750">trac #12750</a>, <a href="http://trac.sagemath.org/sage_trac/ticket/12799">trac #12799</a>

Work issues: 

Reviewers: Martin Albrecht, Jeroen Demeyer, Leif Leonhardy

Merged in: sage-5.0.beta13

Attachments: <ol></ol>