dubious (I don't think 0.0/0.0 == 0.0...) but the result seems to be
correct.
- Documented that soleCubic() and solveQuadratic() are not guaranteed to
return the roots in order, and nor that they are guaranteed to not return
duplicate roots.
git-svn-id: svn://svn.code.sf.net/p/fonttools/code/trunk@431 4cde692c-a291-49d1-8350-778aa11640f8