Dependency on bzrtools should be mentioned in README

bzr-builddeb depends on bzrtools, but this is not mentioned in README under Installation while other dependencies are there.

Btw, it would be nice be able to run the test suite even without bzrtools:

lukas@nemo:~/.bazaar/plugins/stats$ bzr -Derror selftest stats
testing: /home/lukas/projects/bzr/bzr.dev/bzr
   /home/lukas/projects/bzr/bzr.dev/bzrlib (1.6b3 python2.5.2)

bzr: ERROR: exceptions.ImportError: No module named bzrtools.upstream_import

Traceback (most recent call last):
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/commands.py", line 846, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/commands.py", line 797, in run_bzr
    ret = run(*run_argv)
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/commands.py", line 499, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/builtins.py", line 2787, in run
    starting_with=starting_with,
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/tests/__init__.py", line 2531, in selftest
    suite = test_suite(keep_only, starting_with)
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/tests/__init__.py", line 2871, in test_suite
    plugin_suite = plugin.test_suite()
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/plugin.py", line 425, in test_suite
    return self.module.test_suite()
  File "/home/lukas/.bazaar/plugins/builddeb/__init__.py", line 616, in test_suite
    result.addTest(tests.test_suite())
  File "/home/lukas/.bazaar/plugins/builddeb/tests/__init__.py", line 147, in test_suite
    for i in testmod_names]))
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/tests/TestUtil.py", line 92, in loadTestsFromModuleNames
    result.addTests(self.loadTestsFromModuleName(name))
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/tests/TestUtil.py", line 97, in loadTestsFromModuleName
    module = _load_module_by_name(name)
  File "/home/lukas/projects/bzr/bzr.dev/bzrlib/tests/TestUtil.py", line 166, in _load_module_by_name
    module = __import__(mod_name)
  File "/home/lukas/.bazaar/plugins/builddeb/tests/test_import_dsc.py", line 34, in <module>
    from bzrlib.plugins.builddeb.import_dsc import DscImporter, files_to_ignore
  File "/home/lukas/.bazaar/plugins/builddeb/import_dsc.py", line 51, in <module>
    from bzrlib.plugins.bzrtools.upstream_import import (
ImportError: No module named bzrtools.upstream_import