This allows avoiding a symlink loop in the `setup`
script ("packages/_libs/dorodango -> "../..").

While Racket still uses `.mzscheme.sls` as an implementation-specific
suffix for R6RS libraries, any other user-facing interfaces should
refer to it as "racket".

Fixes a bug during bootstrap if (spells foreign) is not ported (e.g. on
Guile).

This file was added in b8d91cff, missing an update to the test suite.

This fixes a bug introduced by commit b8d91cff (Implement library
compilation for Guile).

This library has been moved in spells due to Guile compatiblity issues.

Compile libraries in topological dependency order.

Now during setup of a destination, the package "dorodango-support" is
installed instead of running an arbitrary, destination-specific
procedure.  However, the contents of the dorodango-support package can
be defined by the destination.

Add the following categories intended for a package's private-use files:

- package-programs: Scheme programs
- package-executables: executables
- package-auxiliaries: other auxiliary files

There is now a destination-specific list of hooks run after a package
has been unpacked and its installation hook run.

This facility is used by the FHS destination to create the shell
wrappers for programs, instead of doing that directly upon
installation of these programs.

A nice effect of this change is that each entry in an inventory of a
package maps to exactly one pathname for the destination, instead of
potentially multiple ones.

Its functionality is now subsumed in the new procedure
`destination-script-pathname'.

- The script runners don't need to be in the PATH, and are now moved
  into ${prefix}/lib/dorodango/scripts to avoid cluttering the
  namespace.

- The source directory for the scripts has been moved to allow for
  simply installing all files in that directory during destination
  setup.

- The script runner filename is no longer hardcoded in hooks.sls.

This category is intended to be for files that are required for by
libraries, but are not themselves R6RS libraries, for instance Scheme
code pulled in by `include' macros.