Handle multiple	adjacent backslash-newlines correctly.
Accept a new parameter LIMIT to specify end of input;
this prevents confusion when the input contains '\0' characters.

(collect_expansion): Fix off-by-1 error when searching for `*/'
at end of a comment used for traditional token concatenation.

(macarg1): Fix off-by-1 error when skipping past `*/'
at end of comment.

From-SVN: r11330