Made some classes final.
Summary:
Currently, the linter raises XHP29 warnings for these files because they are not abstract or final.
I guess there are two possibly solutions, either making the classes final or marking them as @concrete-extensible. Given that there are no subclasses of these classes in the phabricator, arcanist and libphutil repositories... I opted to declare the classes as final.
Test Plan:
The following linter warnings are gone:
>>> Lint for src/aphront/configuration/AphrontDefaultApplicationConfiguration.php:
   Warning  (XHP29) Class Not abstract Or final
    This class is neither 'final' nor 'abstract', and does not have a
    docblock marking it '@concrete-extensible'.
               3 /**
               4  * @group aphront
               5  */
    >>>        6 class AphrontDefaultApplicationConfiguration
               7   extends AphrontApplicationConfiguration {
               8
               9   public function __construct() {
>>> Lint for src/applications/differential/mail/DifferentialReplyHandler.php:
   Warning  (XHP29) Class Not abstract Or final
    This class is neither 'final' nor 'abstract', and does not have a
    docblock marking it '@concrete-extensible'.
               1 <?php
               2
    >>>        3 class DifferentialReplyHandler extends PhabricatorMailReplyHandler {
               4
               5   private $receivedMail;
               6Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Differential Revision: https://secure.phabricator.com/D8347