title: mvn release - svn error while tagging
body: <p>While trying to execute the release:prepare goal, I get the following failure :</p>
  
  <pre><code>...
  [INFO] Checking in modified POMs...
  [INFO] SVN commit directory: C:\dev\eclipse\workspace\xxx-parent
  [INFO] Tagging release with the label xxx-parent-0.0.1...
  [INFO] SVN checkout directory: C:\dev\eclipse\workspace\xxx-parent
  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD FAILURE
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time: 16.603s
  [INFO] Finished at: Thu Oct 22 14:43:44 CEST 2015
  [INFO] Final Memory: 10M/244M
  [INFO] ------------------------------------------------------------------------
  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.5.3:prepare (default-cli) on project xxx-parent: Unable to tag SCM
  [ERROR] Provider message:
  [ERROR] SVN tag failed.
  [ERROR] Command output:
  [ERROR] svn: Commit failed (details follow):
  [ERROR] svn: Commit blocked by pre-commit hook (exit code 1) with output:
  [ERROR] A message is mandatory!
  [ERROR] The message must comply to the following structure 'TT 12345: Some explanation'.
  [ERROR] Pay attention to the white space between TT and the TT number and between the colon and the explanation.
  [ERROR] The explanation after the colon should at least be 10 characters long.
  [ERROR] svn: MERGE of '/svn/xxxxx/xxx-parent': 409 Conflict (https://192.19.20.56)
  [ERROR] -&gt; [Help 1]
  ...
  </code></pre>
  
  <p>The project is <strong>well updated in the trunk with the release version</strong> but <strong>not in the TAGS</strong> and it looks like it's trying to do a svn merge ?! Is that it ? If so, why ?</p>
  
  <p>Here is the maven-release-plugin config:</p>
  
  <pre><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;2.5.3&lt;/version&gt;
              &lt;dependencies&gt;
                  &lt;dependency&gt;
                      &lt;groupId&gt;com.google.code.maven-scm-provider-svnjava&lt;/groupId&gt;
                      &lt;artifactId&gt;maven-scm-provider-svnjava&lt;/artifactId&gt;
                      &lt;version&gt;1.6&lt;/version&gt;
                  &lt;/dependency&gt;
              &lt;/dependencies&gt;
              &lt;configuration&gt;
                  &lt;providerImplementations&gt;
                      &lt;svn&gt;javasvn&lt;/svn&gt;
                  &lt;/providerImplementations&gt;
                  &lt;branchBase&gt;https://192.19.20.56/svn/xxxxx/xxx-parent/BRANCHES&lt;/branchBase&gt;
                  &lt;tagBase&gt;https://192.19.20.56/svn/xxxxx/xxx-parent/TAGS&lt;/tagBase&gt;
                  &lt;scmCommentPrefix&gt;TT 00000: Tagging release of project ${project.name} ${project.version}, &lt;/scmCommentPrefix&gt;
              &lt;/configuration&gt;
          &lt;/plugin&gt;
  </code></pre>