title: untabify and remove trailing whitespaces in emacs
body: <p>I'm working on large scale project where in there are ~100 engineers working on many files. I would like to see if I could add customization in emacs to remove trailing white spaces and untabify the lines which i'm editing. It wont be good idea to untabify and remove whitespaces in large files which are not related my changes. (I agree, everyone in the team should be following some basic rules. What to do, sometime it doesn't work in that way. :( ).</p>
  
  <p>Currently I've enabled:</p>
  
  <pre><code>(show-ws-toggle-show-trailing-whitespace)
  (show-ws-toggle-show-tabs)
  </code></pre>
  
  <p>Issue with these options, it makes all over files either yellow or white if owner of the file hasn't fixed his tabs and trailing whitespaces. </p>
  
  <p>It would be great if you could point me to emacs options which will enable me "remove whitespaces and tabs on lines which I'm editing" (not all over the files).</p>