The BonsaiPoller periodically polls a Bonsai server. This is a
CGI script accessed through a web server that provides information
about a CVS tree, for example the Mozilla bonsai server at
http://bonsai.mozilla.org. Bonsai servers are usable by both
humans and machines. In this case, the buildbot's change source forms
a query which asks about any files in the specified branch which have
changed since the last query.
Please take a look at the BonsaiPoller docstring for details about the arguments it accepts.