When checking out from source code, the paths that were used to
configure the project should be carried on to the installed binary,
so the same libraries are used without much effort.
By using RUNPATH instead of (just) RPATH, it can be overridden with
LD_LIBRARY_PATH if the user so desires.
Akin to config.h, we write project-version.h whenever the VCS sha hash
of the project changes. This file can then be included to embed this
into the project. Since this changes more frequently, we choose another
file than config.h. Care is also taken to not rewrite the header if the
information doesn't change, but the project is rebuilt.
