- keep history of installed packages/journal of package transaction,
  so we can roll back to yesterday, or see what got installed in the
  latest yum update.

- signed pkgs

- gzip repository of look-aside pkg xml files somehow?

- transactions, proper recovery, make sure we don't poop our package
  database (no more rm /var/lib/rpm/__cache*).

- diff from one package set to another answers: "what changed in
  rawhide between since yesterday?"

- rewrite qsort and bsearch that doesn't require global context var
  and can output a map describing the permutaion.

- use hash table for package and property lists so we only store
  unique lists (like for string pool).

- use existing, running system as repo; eg

	razor update razor://other-box.local evince

  to pull eg the latest evince and dependencies from another box.  We
  should be able to regenerate a rzr pkg from the system so we can
  reuse the signature from the originating repo.

- Ok, maybe the fastest package set merge method in the end is to use
  the razor_importer, but use a hash table for the properties.  This
  way we can assign them unique IDs immediately (like tokenizing
  strings).

- test suite should be easy, just keep .repo files around and test
  different type of upgrades that way (obsoletes, conflicts, file
  conflicts, file/dir problems etc).  Or maybe just keep a simple file
  format ad use a custom importer to create the .repo files.

- pipelined download and install; download is network bound, install
  is disk bound.  Start installing once we have self-contained set of
  packages.  Install in reverse topo-sort order.  Interruptible
  installation; stops at nearest checkpoint.

- make packages pointers be either an index into the package pool or a
  direct link to a package when there is only one package.  set a high
  bit to indicate which it is.  similar for properties.

- split out hash table code from importer, make the merger use just
  the hash table.