D24259: WIP: Save file directly if possible when root privileges are required

[Alexander Volkov]

volkov added a dependency: D24245: Add support for passing Unix file 
descriptors.

REPOSITORY
  R39 KTextEditor

REVISION DETAIL
  https://phabricator.kde.org/D24259

To: volkov
Cc: kwrite-devel, kde-frameworks-devel, LeGast00n, GB_2, domson, michaelh, 
ngraham, bruns, demsking, cullmann, sars, dhaumann