10.8 Miscellaneous poly_int routines

`print_dec (value, file, sign)'

`print_dec (value, file)'

Print value to file as a decimal value, interpreting the coefficients according to sign. The final argument is optional if value has an inherent sign; for example, poly_int64 values print as signed by default and poly_uint64 values print as unsigned by default.

This is a simply a poly_int version of a wide-int routine.