make sure that the path generators never get stuck in in infinite loop caused by floating point inaccuracies
 define a maximum recursion depth (20) for the PushCutter algorithm (i.e. maximum precision = 1/(1^20) of bounding box width)


git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@156 bbaffbd6-741e-11dd-a85d-61de82d9cad9