Validation to prevent 2 releases with the same version is broken

I believe this is a new bug since the upgrade, tagging as such.

Confirmed two things:

- This is definitely a regression from the D6 port

- It only fails if you have HEAD release at a given version, create a branch for that version, and then create a new release node directly from that branch instead of of editing the HEAD release node and moving that to the new (matching) branch.

E.g. this works:
- DRUPAL-6--1 branch exists
- 6.x-1.x-dev release node exists
- try to make a new release node from HEAD called "6.x-1.x-dev" -- you're stopped with a validation error.

This is the broken case:
- 6.x-1.x-dev release node exists using HEAD
- Create the DRUPAL-6--1 branch
- try to make a new release node from DRUPAL-6--1 called "6.x-1.x-dev" -- in D6 it lets you do this, in D5, you're also stopped.

http://drupal.org/cvs?commit=177894

#386048 by dww: Fixed bug in the validation that is supposed to
prevent users from adding a release node from a branch that has the
same version string as an existing release node from HEAD. Removing
the code that disables the validation would help. ;) I have no idea
how this validation happened in D5, but it did.

Strange... ;) But, I don't feel like spending the time tracking down how this works in D5 -- all I know is it now works in D6, and none of the other cases are broken now in my testing, and that's all I really care about at this point.