D17617: Display error instead of silently failing when asked to create folder that already exists

[Nathaniel Graham]

ngraham marked an inline comment as done.

REPOSITORY
  R241 KIO

REVISION DETAIL
  https://phabricator.kde.org/D17617

To: ngraham, #dolphin, elvisangelaccio
Cc: dfaure, emateli, elvisangelaccio, Codezela, kde-frameworks-devel, michaelh, 
ngraham, bruns