Don't allow read messages to stack

It's annoying when vimdiff outputs the filenames that you just asked it
to open, causing the "Press ENTER ..." message. This change prevents
that from happening, and also stops a similar thing from occurring with
file-line.
Put back nerdtree

As nice as vimfiler is, it has some issues that make it unusable for me
due to the way it uses colons internally:

* It doesn't allow you to edit files with colons in their name.
* It breaks file-line.