Rename it to the more intention revealing NERDTreeRespectWildIgnore.
Use it directly in the `globpath()` call rather than surrounding if
statement. Its subjective, but I find this clearer.
Add an initializer for the option.
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
