D17741: avoid blocking kio_http_cache_cleaner and ensure exit with session

[David Faure]

dfaure accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R241 KIO

REVISION DETAIL
  https://phabricator.kde.org/D17741

To: mkoller, dfaure
Cc: kde-frameworks-devel, michaelh, ngraham, bruns