title: How to customise the tag format of the Maven release plugin?
body: <p>In our SVN repo, we store tags like this:</p>
  
  <pre><code>trunk
      project_a
      project_b
  branches
      project_a
          branch_x
          branch_y
      project_b
  tags
      project_a
          1.0
          1.1
      project_b
          1.0
  </code></pre>
  
  <p>When I run the Maven release plugin's "<a href="http://maven.apache.org/plugins/maven-release-plugin/prepare-mojo.html">prepare</a>" goal on project A, by default it creates the tag as "tags/project_a-x.x", which does not match my tag naming scheme above. I am thus depending upon whoever does the release (i.e. a fallible human) to spot this and change the tag to "tags/project_a/x.x". How can I tell the release plugin to use the correct format by default?</p>
  
  <p>The "prepare" goal has a "<a href="http://maven.apache.org/plugins/maven-release-plugin/prepare-mojo.html#tag">tag</a>" configuration option that claims to do this, but if I set it as follows:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;plugin&gt;
      &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
      &lt;artifactId&gt;maven-release-plugin&lt;/artifactId&gt;
      &lt;version&gt;2.1&lt;/version&gt;
      &lt;configuration&gt;
          &lt;tag&gt;${project.artifactId}/${project.version}&lt;/tag&gt;
      &lt;/configuration&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p>... then the created tag is "tags/project_a/x.x-SNAPSHOT", i.e. it uses the pre-release version number instead of the release version number. Hardcoding the tag name into the POM seems wrong too.</p>
  
  <p>How can I ensure that the tag is correct by default?</p>