pybox2d svn r51

So, I figured I'd detail some of the changes made to pybox2d a bit more in detail here. Here's the changes in r51:

* RayCasts working!
* Fixed some cvar confusion:
Since you can't do dir(box2d.cvar), I added a (mostly complete) list in box2d.cvars:

for c in box2d.cvars:
  print c, getattr(box2d.cvar, c)

will show plenty of information:

b2_pi 3.14159274101
b2_maxManifoldPoints 2
b2_maxPolygonVertices 8
b2_maxProxies 512
b2_maxPairs 4096
b2_linearSlop 0.00499999988824
b2_angularSlop 0.0349065884948
b2_toiSlop 0.0399999991059
b2_maxTOIContactsPerIsland 32
b2_maxTOIJointsPerIsland 32
b2_velocityThreshold 1.0
b2_maxLinearCorrection 0.20000000298
b2_maxAngularCorrection 0.139626353979
b2_maxLinearVelocity 200.0
...