ZRoundup looks only in certain places for its home directory.  In
fact, Zope has a method for contructing an arbitrary list of
directories that it searches for Products (the environment variable
PRODUCTS_PATH).  So to find itself, ZRoundup needs to search that
path.  Fortunately, that path is available from the __path__ property
of the Products object.  The attached diff shows code that works for me.