Use new q ‘format’ flag when fixing quotes in C

Use new q ‘format’ flag when fixing quotes in C

* src/image.c (image_size_error): New function.  All uses of
image_error with "Invalid image size ..."  changed to use it.
* src/image.c (image_size_error, xbm_load_image, xbm_load)
(xpm_load, xpm_load_image, xpm_load, pbm_load, png_load_body)
(jpeg_load_body, tiff_load, gif_load, imagemagick_load_image)
(imagemagick_load, svg_load, svg_load_image, gs_load)
(x_kill_gs_process):
* src/lread.c (load_warn_old_style_backquotes):
* src/xfaces.c (load_pixmap):
* src/xselect.c (x_clipboard_manager_error_1):
Use %qs, not uLSQM and uRSQM.
* src/syntax.c (Finternal_describe_syntax_value):
Prefer Fsubstitute_command_keys to Fformat, as this lets
us use AUTO_STRING.
* src/xdisp.c (vadd_to_log): Use AUTO_STRING on the format argument,
as it's now guaranteed to be ASCII.
* src/xselect.c (x_clipboard_manager_error_2):
Avoid grave accent in low-level stderr diagnostic.