Fix scoping / name look-up issue in PolyBoRi 0.8.0 and support flags from the environment

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/12750">trac #12750</a>.

The following was found out here:
http://groups.google.com/group/sage-release/browse_thread/thread/e2a87c73dc1625f2
```
* PolyBoRi fails to build due to stricter (C++11) scoping / name look-up rules.
    Unfortunately PolyBoRi doesn't honor CXXFLAGS, so I had to use CXX="g++-4.7.0 -fpermissive" to make the spkg build. 
```

The scoping issue should be fixed here:
https://bitbucket.org/brickenstein/polybori/changeset/43b3931ceed7/raw/

Also, we should support CXXFLAGS and CFLAGS (ANd CPPFLAGS?) in the spkg.

=== Current spkg ===
 * **Install** http://boxen.math.washington.edu/home/dreyer/spkg/polybori-0.8.0.p2.spkg

Reported by: AlexanderDreyer

Component: algebra

CC: leif,, PolyBoRi,, malb,, burcin

Report Upstream: Fixed upstream, in a later stable release.

Authors: Alexander Dreyer

Dependencies: 

Work issues: 

Reviewers: Leif Leonhardy

Merged in: sage-5.0.beta12

Attachments: <ol></ol>