Fixed a bug with den == -1 in new _canonicalise code
Fixed a bug with den == -1 in new _canonicalise code

jpflori/flint2,wbhart/flint2,dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,fredrik-johansson/flint2,wbhart/flint2,dsroche/flint2,jpflori/flint2,wbhart/flint2,fredrik-johansson/flint2,jpflori/flint2,dsroche/flint2,dsroche/flint2