- rearrangement of modules, contributed by Gustavo Niemeyer
1) Moved plugins directory to bzrlib/, so that there's a standard plugin directory which is not only installed with bzr itself but is also available when using bzr from the development tree. BZR_PLUGIN_PATH and DEFAULT_PLUGIN_PATH are then added to the standard plugins directory.
2) Moved the needed third-party tools to an internal directory under bzrlib/util. This makes sure that needed tools are available in the bzr installation, including the correct/expected version, and eases the process of packaging and redistribution of bzr ('setup.py bdist*' creates a working distribution).
3) Fixed setup.py including the needed package entries.