Summary:
This will allow KMail to properly communicate the difference also when
using per-folder settings for loading external references. This in turn
makes 746e02af07 also work in that case.
Taken from KDE patches and adapted to TDE.
See https://phabricator.kde.org/D12393 and https://phabricator.kde.org/D12394
Signed-off-by: Slávek Banko <slavek.banko@axis.cz>