* term.c: Integer and memory overflow issues.

* term.c: Integer and memory overflow issues.

(max_frame_lines): Remove; unused.
(encode_terminal_src_size, encode_terminal_dst_size): Now ptrdiff_t,
not int.
(encode_terminal_code, calculate_costs): Check for size
calculation overflow.
(encode_terminal_code): Use ptrdiff_t, not int, to record glyph
table lengths and related sizes.  Don't update size until alloc
done.  Redo calculations to avoid overflow.
(calculate_costs): Don't bother calling xmalloc when xrealloc will do.