This code seems to have accumulated quite some legacy cruft. The
two defines are never set from CMake, thus they get defined to
"false". Now when the PWD contains a file called "false", like is
usually the case for /usr/bin, then kdesu would suddenly stop working.
You just get the super unhelpful "Su returned with an error" dialog
shown...
This patch removes the obsolete macros and always uses QStandardPath
to find the executable path for the superUserCommand. This makes the
code work for me when the PWD contains a file called "false".