* mh-compat.el (mh-image-load-path-for-library): Move here from
mh-utils.el and wrap with mh-defun-compat since this function will be
soon added to image.el.
* mh-utils.el (mh-image-load-path-for-library): Move to mh-compat.el.
(mh-normalize-folder-name): Add return-nil-if-folder-empty argument
which is useful when calling mh-normalize-folder-name to process the
folder argument for the folders command.
(mh-sub-folders): Use new flag to mh-normalize-folder-name to make
this function more robust. It could too easily list the folders in /.
(mh-folder-list): Fix a couple of problems pointed out by Thomas
Baumann. Set folder to nil if empty. Don't append "/" if folder nil.