vim: gracefully handle undotree, NERDtree etc when killing syntax
vim: gracefully handle undotree, NERDtree etc when killing syntax

Follow-up to: https://github.com/wincent/wincent/issues/37

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent