Bitmap::is_path_a_supported_image_format() and Bitmap::load_from_file()
now check the file extension with CaseSensitivity::CaseInsensitive.
This fixes a couple of inconsistencies, for example would
FileSystemModel::icon_for() recognize image files uppercase extensions
but couldn't create thumbnails for them (any attempt to create a bitmap
from such files would fail).
5b68ea8dde