* the XML cache doesn't include all packages (e.g. ubuntu-font-family/automake)
  - there is probably bugs in the tool ('ticache') that generates the cache.
* should support system model
  - don't use conary API directly in conaryBackend.py
  - move self.xmlcache into conarypk, so it won't come in the way of system
    model support.
  - implement search (pending upcoming features of conary)
* fix use of post_process and implement _pkg_compare in conaryFilter.py
  - http://lists.freedesktop.org/archives/packagekit/2011-March/006245.html
* simplify _resolve_list(). It calls conary API directly and has much
  duplication with resolve().
  - _show_package_list() has duplication with the newly added _show_packages()
  - the data structure dict(trove, metadata) (as used in _show_package_list())
    is too complicated than necessary.
* decide what to do with package components
* don't show dead packages:
  - version == '0'
* conarypk.py: move _classic_build_update_job()/_classic_get_package_update()/_classic_get_updateall_job()
  out of the ConaryPk and change them into functions, as the _model* functions.
