title: Vimscript check if current buffer has unsaved changes
body: <p>I currently have my status line set up so that it's orange in insert mode and white otherwise. I'd like to make it go another color when I drop back to normal mode if the file has any unsaved changes, as I regularly take a little walk down a rabbit hole wondering why my changes have not taken effect. The little "[+]" doesn't smack me in the face enough ;)</p>
  
  <p>I can't find any functions that start with "buf" and look like predicates for dirtiness though. I assume one exists, but is named something else. I expect there to be something like <code>bufdirty()</code> or <code>bufchanged()</code>. Any pointers? :)</p>