as recently mused over on the plasma-devel list. nobody really knows
why it's not installed to bindir and at the same time various
distributions manually symlink it there because they think it is useful.
from a scripting POV it certainly makes more sense to have the tool in bin
as libexec may not be easily resolvable (32bit vs 64bit vs architecture
triplets on various distributions).
by default we'll now symlink kdesu to the bindir under the name kdesu5
(so as to not conflict with kdelibs4's kdesu).
this feature can be opted out of by setting KDESU_SYMLINK=OFF