log2changes: correct command line, fix tag usage, change Version output

--decorate=full is needed with my git 1.7.1 to get the necessary
output so that the previous edit would work to extract the
Version stuff.

... but I had to edit how the refs/tags was extracted since it
had a little flaw that made it miss the 7.20.1 output.

Finally, I changed so that Version is outputted even more similar
to how CHANGES does it.