Fix Maven Javadoc generation problem

There is a serious problem with the Maven Javadoc plugin. Please see
http://jira.codehaus.org/browse/MJAVADOC-275
for details. This problem is fixed by using maven-javadoc-plugin V2.7
instead of maven-javadoc-plugin v2.6.1.

pom.xml

@@ -194,7 +194,7 @@
 	<plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
-	  <version>2.6.1</version>
+	  <version>2.7</version>
         </plugin>
 
         <plugin>