Overflow, signedness and related fixes for images.

Overflow, signedness and related fixes for images.

* dispextern.h (struct it.stack[0].u.image.image_id)
(struct_it.image_id, struct image.id, struct image_cache.size)
(struct image_cache.used, struct image_cache.ref_count):
* gtkutil.c (update_frame_tool_bar):
* image.c (x_reference_bitmap, Fimage_size, Fimage_mask_p)
(Fimage_metadata, free_image_cache, clear_image_cache, lookup_image)
(cache_image, mark_image_cache, x_kill_gs_process, Flookup_image):
* nsmenu.m (update_frame_tool_bar):
* xdisp.c (calc_pixel_width_or_height):
* xfns.c (image_cache_refcount):
Image IDs are now ptrdiff_t, not int, to avoid arbitrary limits
on typical 64-bit hosts.

* image.c (RANGED_INTEGERP, TYPE_RANGED_INTEGERP): New macros.
(x_bitmap_pixmap, x_create_x_image_and_pixmap):
Omit unnecessary casts to int.
(parse_image_spec): Check that integers fall into 'int' range
when the callers expect that.
(image_ascent): Redo ascent calculation to avoid int overflow.
(clear_image_cache): Avoid overflow when sqrt (INT_MAX) < nimages.
(lookup_image): Remove unnecessary tests.
(xbm_image_p): Locals are now of int, not EMACS_INT,
since parse_image_check makes sure they fit into int.
(png_load, gif_load, svg_load_image):
Prefer int to unsigned where either will do.
(tiff_handler): New function, combining the cores of the
old tiff_error_handler and tiff_warning_handler.  This
function is rewritten to use vsnprintf and thereby avoid
stack buffer overflows.  It uses only the features of vsnprintf
that are common to both POSIX and native Microsoft.
(tiff_error_handler, tiff_warning_handler): Use it.
(tiff_load, gif_load, imagemagick_load_image):
Don't assume :index value fits in 'int'.
(gif_load): Omit unnecessary cast to double, and avoid double-rounding.
(imagemagick_load_image): Check that crop parameters fit into
the integer types that MagickCropImage accepts.  Don't assume
Vimagemagick_render_type has a nonnegative value.  Don't assume
size_t fits in 'long'.
(gs_load): Use printmax_t to print the widest integers possible.
Check for integer overflow when computing image height and width.