Store directories names without slash symbol

This is a start, now need to find what's broken now and fix it.
Fix cursor positioning after going updir
Less duplication in show_bookmarks_menu()
Fix navigation to directories via bookmarks

This slightly changes approach with regard to how names with slashes
stored/displayed.

Before:
 * store as is
 * display as is

Now:
 * strip trailing slash on storing
 * add trailing slash on displaying for existing directories
Remove chosp() on file search

Isn't needed anymore.
Fix local filtering of directories via trailing /
Introduce bookmarks:NO_BOOKMARK_FILE

Special file name value for "directory bookmarks".
Update literals "../" => ".."
Remove unneeded calls to chosp()
Merge branch 'remove-trailing-slash-from-dir-name'

Don't store trailing slashes in names of directory entries.