title: Flask default error handler not being called
body: <p>I have an <code>errors.py</code> module to map errors to templates. I was wanting to add a default error handler and came across: <a href="http://flask.pocoo.org/mailinglist/archive/2012/7/12/default-error-handler/#cbeb8809dc0da7133f14b99e16f31d6b" rel="noreferrer">http://flask.pocoo.org/mailinglist/archive/2012/7/12/default-error-handler/#cbeb8809dc0da7133f14b99e16f31d6b</a></p>
  
  <p>I'm using <code>Blueprint</code> to modularize things and the errors module has the following mappings:</p>
  
  <pre><code>@err.app_errorhandler(403)
  def forbidden(e):
     return render_template('403.html'), 403
  
  @err.app_errorhandler(500)
  def serverError(e):
     return render_template('500.html'), 500
  
  @err.app_errorhandler(Exception)
  def defaultHandler(e):
     return render_template('defaultError.html'), e.code
  </code></pre>
  
  <p>The specific mappings (403, 500) work fine if I abort to them (or induce them naturally), but if I abort to anything else (404 etc.) the <code>defaulHandler()</code> is not invoked.</p>