Lock down maven plugin versions

This prevents surprises by implicit updates to newer versions.

Change-Id: I06508036d468fa5299ea774e26a73312bb286ec2
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

pom.xml

       <plugins>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
-          <artifactId>maven-jar-plugin</artifactId>
+	  <artifactId>maven-jar-plugin</artifactId>
+          <version>2.3</version>
           <configuration>
             <archive>
               <manifestEntries>
           <version>2.1</version>
         </plugin>
 
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-source-plugin</artifactId>
+          <version>2.1.1</version>
+        </plugin>
+
+	<plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-javadoc-plugin</artifactId>
+	  <version>2.6.1</version>
+        </plugin>
+
         <plugin>
           <groupId>org.codehaus.mojo</groupId>
           <artifactId>build-helper-maven-plugin</artifactId>