QtIFW

fix error handling in 7z lib

 - remove an already existing symlink at extraction, because it uses
   QFile to get the io device and that would be the symlink target
   which was wrong.
 - try to get better 7z error output
 - an error would be now: "There was a problem while performing the
   operation: Error while extracting 'C:\Qt\qtcreator-2.7.0_test.7z':
   Cannot open file: D:/test/qtcreator-2.7.0_test/bin/sqldrivers/qsqlite4.dll
   (Access is denied.)"
 - move setPermissions to the end so read only files are getting the right timestamp

Change-Id: I8881144660296618d443568e6974bf2721328991
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>