Image loading speedup
* glom/libglom/sharedptr.h: Added operator!=. * glom/mode_data/flowtablewithfields.h: * glom/mode_data/flowtablewithfields.cc: Added set_other_field_value which is the same as set_field_value except that it does not set the value for widget that belongs to the passed layout item's widget itself. This can be used if that very widget already contains the new value to avoid setting it again. Especially when dealing with large images this brings an essential speedup. * glom/mode_data/box_data_details.cc (on_flowtable_field_edited): Use set_other_field_value, so that we don't set the value for the field which the user already changed again. * glom/utility_widgets/imageglom.h: * glom/utility_widgets/imageglom.cc: Store the original data of the image file, and return it in get_value(), instead of creating a PNG from the raw image data, to speed up loading a large image file. * glom/utils_ui.cc (get_pixbuf_for_gda_value): When loading images from the database, allow all image types, not just PNGs. * glom/xsl_utils.cc: Include gtk/gtk.h to fix the build for me.