Provide an option to create a branch for maintenance releases

This email thread prompted this issue: http://www.mail-archive.com/users@maven.apache.org/msg65485.html

As I [Heinrich Nirschl] see it there are two solutions:
1) starting the maintenance branch before the release and doing the
release on the branch, in this case you have to manually adjust the
version on the trunk.

2) doing the release on the trunk and starting the maintenance branch
from the tagged version, in this case the version has to be manually
updated on the branch.

Both approaches work, but there is some manual version editing in
both. Once the branching is done, the release plugin works fine on the
branch (for releasing further maintenance releases) and on the trunk
(for releasing the next major release). The manual update is only
necessary once per branch.