yyless(n) macros

[Bruce Lilly]

The parameter in the definitions of the yyless macros
produced by flex 2.5.24 (and probably some earlier
versions) is not protected, so e.g. the following leads
to a compilation error:

...
char *c, *s = yytext;
c = strchr(s, ':');
yyless(c - s);

The difference between two pointers of like type is
a valid integral expression; the problem is that the
macro expansion does not enclose the parameter "n" in
parentheses, so an invalid exprssion results from the
macro expansion.