through config.h, to prevent silly Autoconf problems.

  archives (using the package in corepkgs/nar).
* queryPathByHash -> expandHash, and it takes an argument specifying
  the target path (which may be empty).
* Install the core Fix packages in $prefix/share/fix.  TODO: bootstrap
  Nix and install Nix as a Fix package.

* Run `test' on `make check'.

* Cleaned up command-line syntax.

  build action for `system' packages (like system.fix) that have
  dependencies on all packages we want to activate.

  So the command sequence to switch to a new activation configuration
  of the system would be:

    $ fix -i .../fixdescriptors/system.fix
    ...
    system.fix -> 89cf4713b37cc66989304abeb9ea189f

    $ nix-switch 89cf4713b37cc66989304abeb9ea189f

* A nix-profile.sh script that can be included in .bashrc.

  nix-instantiate.

* Fixed the register script.