Adjust installation tools to support cross-installation (i.e.,
installation for a platform other than the current one) as triggered
by "system.rktd" in "lib" having different information than the
running Racket executable.
When a package "p" is clone-linked and the repo for "p" changes to be
a multi-package repository (e.g., with "p-lib", "p-doc", and "p"), a
`raco update` would get confused. Unofrtunately, a plain `raco pkg
update p` can't work in that case, because the clone link would still
be a pathless repo URL; the repairs make `raco pkg update --lookup
--clone ..../p` work as is should.
Related: fix inference of package names in the early check for whether
a package is installed.
Packages that are installed as other than a link are not meant to be
edited, but work can get lost if a package is edited and then removed
or updated. Avoid that work loss by moving removed or updated packages
to a trash folder.
By default, the trash folder holds up to 512 packages for up to 48
hours. To disable the trash folder (for a given scope), use
raco pkg config --set max-trash-packages 0
(I expect that some variant of Greenspun's rule predicted the eventual
inclusion of "backup" management in the package system.)
