Version's %m handles PODNAME; value-from-comment code in own role

This changeset allows the Version section to handle %m when only a PODNAME is
available, as in scripts.  This both causes it to behave as the Name section
does in such a scenariao, but also to be used with scripts w/o having to do
any extraordinary effort to make it work.

The "get a string from a comment" code is also refactored out into its own
helper role so as to be able to share it between the Name and Version plugins,
as well as make it available for any interested third-party packages.