this commit is a modified patch from Guillaume Duranceau

this commit is a modified patch from Guillaume Duranceau

this way we can e.g. not show the git submenu unless a git repo is
actually present

previously the code didnt take &hidden (it assumed it was set) into
account when determining if splitting was needed when using the o
mapping on a file node

Previously every time the tree window was created a new [no-name] buffer
was being created (visible with :ls!). Avoid this by creating the window
with split,  not new

this is because of vims fucking stupid functionality where ignorecase
changes the way == behaves. It was causing bugs when the user had
ignorecase set.

now we can go   vim  <some dir>   and it loads up a nerd tree instead of
a netrw

when the user activate the   ../ (up a dir)   line or hit U or U it
wasnt changing vims CWD when NERDTreeChDirMode==2

allows the statusline to be customised for the nerd tree window

Path.New was expecting an absolute path. Now we convert paths to
absolute inside Path.New