Fixed inclusion of sumdiff_n from mpir.
Fixed inclusion of sumdiff_n from mpir.

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