that typedef 'short'. 'char' (which was previously used) because char
may be unsigned and ((char)EOF) != EOF if that is the case. That was
causing the (char)EOF (0xff) pushed back in main to be interepreted as
a character, and, in some cases, to be written to the output. 'short'
was used rather than 'signed char' because if the latter is used,
0xff characters in the input would confuse m4. (No point in introducing
(more?) 8-bit lossage.)
