Revert "upgrade maven-release-plugin"

This reverts commit acef92c4.
2.2.2 has http://jira.codehaus.org/browse/MRELEASE-724 and it prevents
me from running a release.

pom.xml

@@ -487,7 +487,7 @@ THE SOFTWARE.
       </plugin>
       <plugin>
         <artifactId>maven-release-plugin</artifactId>
-        <version>2.2.2</version>
+        <version>2.1</version>
         <configuration>
           <!-- enable release profile during the release, create IPS package, and sign bits. -->
           <prepareVerifyArgs>-P release,sign</prepareVerifyArgs>