Validate tagBase before starting

Please note I'm using Subversion. I guess this tagBase validation isn't necessary with some other systems (like the old CVS).

Currently, Maven-release-plugin proceeds this way:

1. Modify the current pom
2. Commit it
3. Tag it (say copy it under the tagBase)
4. Go back to next dev version

The thing is: if the tagBase directory doesn't exist (forgotten or because of a typo in the pom), release:prepare will fail when trying to tag ALTHOUGH it already has committed the modified version :-/.

I think that before starting prepare (or at least, there should be an option for it), release-plugin should check (using a "svn list [tagBase]" for example, in the case of Subversion) it the given tagBase exists. It would prevent from surely going into the wall when the tagBase is actually incorrect.

Thanks a lot!

Cheers.