Integer and memory overflow issues (Bug#9196).
+ * buffer.c (overlay_str_len): Now ptrdiff_t, not EMACS_INT,
+ since either will do and ptrdiff_t is convenient with xpalloc.
+
* charset.c (charset_table_size)
(struct charset_sort_data.priority): Now ptrdiff_t.
(charset_compare): Don't overflow if priorities differ greatly.