process is already holding a lock on a path, it may acquire the lock
  again without blocking or failing).  (This might be dangerous, not
  sure).  Necessary for fast builds to work.

  a regular file.  I.e., `nix-hash --flat' is equivalent to the
  coreutils `md5sum' command (which doesn't exist on all systems).

* Allow booleans in package environment bindings (True maps to "1",
  False maps to "").

  the same time.

  normalise to Nix expression.

  normal form in a single transaction to ensure that if we crash,
  either everything is registered or nothing is.  This is for
  recoverability: unregistered paths in the store can be deleted
  arbitrarily, while registered paths can only be deleted by running
  the garbage collector.

* Simplified realiseSlice().

  ensuring that simultaneous invocations of Nix don't clobber
  each other's  builds.

* Fixed a bug in `make install'.

* Open all database tables (Db objects) at initialisation time, not
  every time they are used.  This is necessary because tables have to
  outlive all transactions that refer to them.

* Checkpoint on exit.

  transaction support (but we don't actually use transactions yet).

  remains set.

  use `--query --generators' anymore.

  Renamed `fstateRefs' to `fstateRequisites'.  The semantics of this
  function is that it returns a list of all paths necessary to realise
  a given expression.  For a derive expression, this is the union of
  requisites of the inputs; for a slice expression, it is the path of
  each element in the slice.  Also included are the paths of the
  expressions themselves.  Optionally, one can also include the
  requisites of successor expressions (to recycle intermediate
  results).

* `nix-switch' now distinguishes between an expression and its normal
  form.  Usually, only the normal form is registered as a root of the
  garbage collector.  With the `--source-root' flag, it will also
  register the original expression as a root.

* `nix-collect-garbage' now has a flag `--keep-successors' which
  causes successors not to be included in the list of garbage paths.

* `nix-collect-garbage' now has a flag `--invert' which will print all
  paths that should *not* be garbage collected.

  this more efficient.
* A flag `-n' in 'nix --query' to normalise the argument.  Default is
  not to normalise.

* Some minor refactoring.

  dynamically links against libdb4 (?!), due to LD_LIBRARY_PATH it picks 
  up our libdb4 instead of SuSE's libdb4, but our libdb4 uses another 
  glibc so loading barfs.

  Instead, all packages should use rpaths to store library locations in
  executables/libraries.  The disadvantage is that overriding rpaths is 
  harder.  (It is possible by invoking the dynamic linker directly, e.g., 
  `/lib/ld-linux.so.2 --ignore-path LIST program args...' to ignore the 
  rpath for the libraries in LIST).  It would be better to use DT_RUNPATH, 
  which is consulted by the dynamic linker *after* LD_LIBRARY_PATH but 
  *before* ld.so.cache and the system directories.

* `nix --query --graph' to print a dot dependency graph of derive
  expressions.

  instead (e.g., `-vvvv' for lots of output).  Default is to only
  print error messages.

  to reach the disk at all.  Looks like a bug.

  up to the given verbosity levels.  These currently are:

    lvlError = 0, 
    lvlNormal = 5,
    lvlDebug = 10,
    lvlDebugMore = 15

  although only lvlError and lvlDebug are actually used right now.