inherit versions for some maven plugins from parent pom,

effectively bumping maven-release-plugin from 2.0-beta-9 to 2.1,
and maven-javadoc-plugin from 2.2 to 2.7 (there was a comment
here that 2.3 caused some release problem so sticking with 2.2..
hopefully 2.7 will be ok)

plugins/pom.xml

@@ -14,7 +14,7 @@
   <packaging>pom</packaging>
 
   <properties>
-    <!-- if your java.net user name is different from local user name, specify it here -->
+    <!-- if your jenkins-ci.org user name is different from local user name, specify it here -->
     <java.net.id>${user.name}</java.net.id>
   </properties>
 
@@ -120,7 +120,7 @@
       <plugin>
         <groupId>org.jenkins-ci.tools</groupId>
         <artifactId>maven-hpi-plugin</artifactId>
-        <version>1.64</version>
+        <!-- version specified in parent pom -->
         <extensions>true</extensions>
         <configuration>
           <showDeprecation>true</showDeprecation>
@@ -134,7 +134,7 @@
       </plugin>
       <plugin>
         <artifactId>maven-release-plugin</artifactId>
-        <version>2.0-beta-9</version>
+        <!-- version specified in parent pom -->
         <configuration>
           <goals>deploy</goals>
         </configuration>
@@ -156,12 +156,8 @@
         </executions>
       </plugin>
       <plugin>
-        <!--
-          javadoc plugin 2.3 apparently interferes with the release process,
-          so sticking to 2.2 (http://www.nabble.com/description-setting-plugin-tp14846399p14950047.html)
-        -->
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>2.2</version>
+        <!-- version specified in parent pom -->
       </plugin>
       <plugin>
         <groupId>org.codehaus.groovy.maven</groupId>