title: Maven release plugin ignores releaseVersion attribute
body: <p>I'm trying to create a svn branch from the trunk which has the version of <code>TRUNK-SNAPSHOT</code> in its pom and children's pom files with this <a href="http://maven.apache.org/maven-release/maven-release-plugin/branch-mojo.html" rel="nofollow">command</a>:</p>
  
  <p><code>mvn --batch-mode release:branch -DbranchName=15.1 -DupdateBranchVersions=true -DupdateWorkingCopyVersions=false -DreleaseVersion=15.1</code></p>
  
  <pre><code>However I'm getting this error:
  [ERROR] BUILD ERROR
  [INFO] ------------------------------------------------------------------------
  [INFO] Error parsing version, cannot determine next version: Unable to parse the version string: "TRUNK-SNAPSHOT"
  </code></pre>
  
  <p>While it's obvious that it was not able to calculate the next version of <code>TRUNK-SNAPSHOT</code>, why would the plugin ignore the <a href="http://maven.apache.org/maven-release/maven-release-plugin/branch-mojo.html#releaseVersion" rel="nofollow">releaseVersion</a> argument that I wanted it to use for the new branch instead of trying to calculate the next version from the trunk's version identifier? </p>
  
  <p>Although running in interactive mode allows me to provide the version for the new branch, I'll need it work in the batch mode. Is there any other way I can specify the new branch version in the batch mode regardless of what the branching source (trunk) version is?</p>
  
  <p><strong>Update 1:</strong> The plugin version I use is <code>2.0-beta-8</code></p>