database and store.

  number of bytes, e.g., in case of a signal like SIGSTOP.  
  This caused `nix --dump' to fail sometimes.

  Note that this bug went unnoticed because the call to `nix 
  --dump' is in a pipeline, and the shell ignores non-zero 
  exit codes from all but the last element in the pipeline.  
  Is there any way to check the result of the initial elements
  in the pipeline?  (In other words, is it at all possible to 
  write reliable shell scripts?)

  input path is referenced in an output paths, we also have to 
  add all ids referenced by that input path.
* Better debug assertions to catch these sorts of errors.

* Fix -qp query.

  This is not entirely trivial since this introduces the possibility
  of mutual recursion.
* Made normal forms self-contained.
* Use unique ids, not content hashes, for content referencing.

  opposed to declared references.  This prunes the reference
  graph, thus allowing better garbage collection and more
  efficient derivate distribution.

  through config.h, to prevent silly Autoconf problems.

  etc. correctly.
* Fixed nix-switch.

  returning different paths if the hash of the path to be added was
  already available in the store under a different name).

  number of bytes in one call).

  Unifying substitutes and successors isn't very feasible for now,
  since substitutes are only used when no path with a certain is
  known.  Therefore, a normal form of some expression stored as a
  substitute would not be used unless the expression itself was
  missing.

  hash for which no local expansion is available, Nix can execute a
  `substitute' which should produce a path with such a hash.

  This is policy-free since Nix does not in any way specify how the
  substitute should work, i.e., it's an arbitrary (unnormalised)
  fstate expression.  For example, `nix-pull' registers substitutes
  that fetch Nix archives from the network (through `wget') and unpack
  them, but any other method is possible as well.  This is an
  improvement over the old Nix sharing scheme, which had a policy
  (fetching through `wget') built in.

  The sharing scheme doesn't work completely yet because successors
  from fstate rewriting have to be registered on the receiving side.
  Probably the whole successor stuff can be folded up into the
  substitute mechanism; this would be a nice simplification.

  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.

  include the paths of the subterms.

  expressions for identical inputs.

  (i.e., it doesn't use realpath(3), which is broken in any case).
  Therefore it doesn't resolve symlinks.

* Use a temporary directory for build actions.