title: maven-datanucleus-plugin fails to enhance classes
body: <p>I get the following at the end of <code>datanucleus:enhance</code> step:</p>
  
  <pre><code>DataNucleus Enhancer completed with success for 0 classes. Timings : input=103 ms, enhance=0 ms, total=103 ms. Consult the log for full details
  DataNucleus Enhancer completed and no classes were enhanced. Consult the log for full details
  </code></pre>
  
  <p>I verified that target directory is listed in the CLASSPATH: <code>WEB-INF/classes</code></p>
  
  <p>The individual class files are present under <code>WEB-INF/classes/com/company/*/*.class</code></p>
  
  <p>Here is the plugin declaration:</p>
  
  <pre><code>        &lt;plugin&gt;
              &lt;groupId&gt;org.datanucleus&lt;/groupId&gt;
              &lt;artifactId&gt;maven-datanucleus-plugin&lt;/artifactId&gt;
              &lt;version&gt;3.2.0-m1&lt;/version&gt;
              &lt;configuration&gt;
                  &lt;api&gt;JDO&lt;/api&gt;
                  &lt;props&gt;${basedir}/datanucleus.properties&lt;/props&gt;
                  &lt;verbose&gt;true&lt;/verbose&gt;
                  &lt;enhancerName&gt;ASM&lt;/enhancerName&gt;
              &lt;/configuration&gt;
              &lt;executions&gt;
                  &lt;execution&gt;
                      &lt;phase&gt;process-classes&lt;/phase&gt;
                      &lt;goals&gt;
                          &lt;goal&gt;enhance&lt;/goal&gt;
                      &lt;/goals&gt;
                  &lt;/execution&gt;
              &lt;/executions&gt;
              &lt;dependencies&gt;
                  &lt;dependency&gt;
                      &lt;groupId&gt;org.datanucleus&lt;/groupId&gt;
                      &lt;artifactId&gt;datanucleus-api-jdo&lt;/artifactId&gt;
                      &lt;version&gt;4.1.0-m1&lt;/version&gt;
                  &lt;/dependency&gt;
              &lt;/dependencies&gt;
          &lt;/plugin&gt;
  </code></pre>
  
  <p>Why is datanucleus enhance plugin not recognising the class files even when CLASSPATH is correct?</p>