Add a hook to `raco setup` to make copies of installed executables,
where the copies start with the configuration or addon directory
of creation time, instead of the default installation or user-specific
path.
Although the same effect can be achived by setting environment
variables such as PLTADDONDIR, tethered executables can be easier
to work with and compose better with other programs.
See also #1206 for some discussion, although this change does
not exactly address the original idea there.
