Fix release.py to allow uncommented initial _VERSION.

Fix release.py to allow uncommented initial _VERSION.

I was in favor of always leaving _VERSION commented in the trunk,
since released branches should fork off the trunk:

  trunkA -> trunkB -> trunkC -> trunkD
   `-> 1.0.0           `-> 1.1.0
        `-> 1.0.1           `-> 1.1.1

But that doesn't seem to have been how things have worked out in BE.
In any case, you will need to release on top of a previous release
(e.g. 1.0.1 on top of 1.0.0 in my above example), so we cannot depend
on an initial comment character before _VERSION.