Fix message aggregation by date.
Fix message aggregation by date.

As reviewed and approved at http://reviewboard.kde.org/r/2521/

This commit fixes SC 4.4.  Fix for trunk will be held until kmail trunk is
unfrozen after merge of akonadi-ports.

CCBUG: 179076

svn path=/branches/KDE/4.4/kdepim/; revision=1073169

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