setup.py breaks if bzr not installed

[Gary van der Merwe]

When building the windows installers, I don't have bzr installed in python (so that I don't accidentally pull modules from the wrong version into the installer.)

In bzr-fastimport 0.10.0, there are some changes to setup.py. These break if bzr is not installed:

### Installing bzr-fastimport ###
Changing directory to c:\Users\garyvdm\bzr\windows-installers-trunk\build-win32/
bzr-fastimport/bzr-2.3
Running c:\Python26\python.exe setup.py install -O1 --install-lib=c:\Users\garyv
dm\bzr\windows-installers-trunk\build-win32/releases/bzr-2.3 ...
Traceback (most recent call last):
  File "setup.py", line 6, in <module>
    from bzrlib import _format_version_tuple
ImportError: No module named bzrlib

For Bazaar 2.3.1, I've installed bzr so as to avoid a delay in getting the installers out, but I would like to revert to not needing to having bzr installed in the future