* lread.c: Integer overflow issues.

* lread.c: Integer overflow issues.

(saved_doc_string_size, saved_doc_string_length)
(prev_saved_doc_string_size, prev_saved_doc_string_length):
Now ptrdiff_t, not int.
(read1): Don't assume doc string length fits in int.  Check for
out-of-range doc string lengths.
(read_list): Don't assume file position fits in int.