Automatically quit vim if NERDTree is last and only buffer

A script to do exactly this has been posted on the NERDTree issue list. Checkout issue-21 on GitHub for nerdtree.

This leads to the single line command for your vimrc here:

autocmd bufenter * if (winnr("$") == 1 && exists("b:NERDTree") && b:NERDTree.isTabTree()) | q | endif