Add back 'v' prefix to version output by print-version (#1473)
Add back 'v' prefix to version output by print-version (#1473)

So that the version used for commit messages and Git tags for new
releases is of form `vN.N.N` not `N.N.N`, for consistency with previous
releases. The 'v' was inadvertently removed as part of #1372.
mozilla-neutrino/neutrino-dev,mozilla-neutrino/neutrino-dev,edmorley/neutrino-dev,edmorley/neutrino-dev