Store version info for this BE installation. By default, use the bzr-generated information in _version.py, but allow manual overriding by setting _VERSION. This allows support of both the “I don’t want to be bothered setting version strings” and the “I want complete control over the version strings” workflows.
Returns the version string for this BE installation. If verbose==True, the string will include extra lines with more detail (e.g. last committer’s name, etc.).