corrected problem with print functions in expressions

added a temporary check for if the command stack (which is not used with
the new translator routines) is not empty in findCode() before checking
for a print function

added missing entries (specifically for the none data type) to the data
type conversion table, which contain invalid codes, so that the table is
not access beyond its bounds

added additional statements with invalid print functions to translator
test #3 (note: old translator does not correctly report errors for these
so tests fail when using old translator)