Add a "Don't ask again" checkbox to "Empty subject"-warning.
Add a "Don't ask again" checkbox to "Empty subject"-warning.

svn path=/trunk/kdenetwork/kmail/; revision=124631

lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi