Admin Settings UI won't reset Outbound Mail settings if memcache is active

If CiviCRM is using memcache for Core_Utils_Cache, you cannot reset the mail settings.

You can reproduce this by doing the following:

1. Make sure you configure CiviCRM to use memcache in civicrm.settings.php
2. Go to Adminstration / Settings / Settings - Outbound Mail, and make a change to your settings; save. Notice that the screen message indicates everything worked fine.
3. Since this will return you to the parent screen, choose "Settings - Outbound Mail", and look at your settings.
4. Alas and alack, your settings have reverted, and your changes have been ignored.

The fix for this is very simple: call CRM_Utils_System::flushCache() at the beginning of the postProcess() routine. Compare CRM_Admin_Form_OptionGroup, which does this right.

I saw this on 4.1.5, but the fix is still needed in the trunk as of today.

A patch will be attached to this issue shortly.