Added test code for scalar_addmul_fmpz.c.
Added test code for scalar_addmul_fmpz.c.

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