title: Postgresql constraint to check for non-ascii characters
body: <p>I have a Postgresql 9.3 database that is encoded 'UTF8'.  However, there is a column in database that should never contain anything but ASCII.  And if non-ascii gets in there, it causes a problem in another system that I have no control over.  Therefore, I want to add a constraint to the column.  Note: I already have a BEFORE INSERT trigger - so that might be a good place to do the check.  </p>
  
  <p>What's the best way to accomplish this in PostgreSQL?</p>