Fix the "TreeDirNode.open()" method
Fix the "TreeDirNode.open()" method

Issues #547 and #526 reported a problem with the "open()" method in
the "TreeDirNode" class.

Specifically, opening a cascade in the NERDTree will perform the
opening operation on the tail of the cascade. This is a problem when
other operations (such as the "u" mapping) close intermediate
cascaded directories, which causes opening the tail to have no
effect (other than toggling the arrow).

Here, the "open()" method was modified to open all directories in a
cascade whenever the tail is opened. This is the only reasonable fix
for this type of problem.

Fixes #547 and fixes #526.

tschundler/dotfiles,tschundler/dotfiles,tschundler/dotfiles