Previously, exiting the NERDTree menu with "Ctrl-C" or "Esc" would
leave the last line of the menu visible. We can avoid this by
redrawing the screen when the menu is aborted in this manner.
On some new versions of vim these files were being loaded before the
main NERD_tree.vim which was causing errors as dependencies werent
loaded in time. Move the classes into lib - so vim wont try to load them
until we tell it
