Added the code from David Zeleznik to clear caches on plugin:install.

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@113048 13f79535-47bb-0310-9956-ffa450edef68

plugin/plugin.jelly

@@ -24,6 +24,15 @@
     <copy file="${maven.build.dir}/${maven.final.name}.jar"
       todir="${maven.home}/plugins"/>
 
+    <delete includeEmptyDirs="true" verbose="false">
+      <fileset dir="${maven.home}/plugins">
+        <include name="*.cache"/>
+        <include name="**/.processed" />
+        <include name="${pom.artifactId}-*/**" />
+        <exclude name="${maven.final.name}.jar" />
+      </fileset>
+    </delete>
+    
   </goal>
 
   <goal name="plugin:deploy" prereqs="plugin"