title: Raise git warning in pre-commit hook
body: <p>I've been using the pre-commit hooks in git to check for problems when I or someone else commits to a project at work.  I can exit with a non-zero status to indicate that the commit has serious problems that should be fixed immediately.</p>
  
  <p>However, sometimes the problem is only something that the programmer needs a warning about (such as they need to update the help file, based on their change, for example).  Is there any way for me to raise a git warning like the one you get with "LF will be replaced by CRLF" for example?  Part of my motivation is that a few of us use SmartGit, so a warning shows up there clearly in yellow.</p>
  
  <p>The post-commit hook looked promising but after trying different return values it never really gave me a warning either.  It would be nice to keep everything in the pre-commit hook, and I'm sure there are better ways to do this.  Thanks for any tips you can give!</p>