Clean arithmetic() function
Clean arithmetic() function

There were some comments and some small bugs in this function
,
as for example accept FTN types in this expressions.

k0gaMSX/scc,8l/scc,k0gaMSX/scc,8l/scc,k0gaMSX/kcc,8l/scc,k0gaMSX/kcc,k0gaMSX/scc