Fixed building single plugins after clean.

git-svn-id: http://svn.igniterealtime.org/svn/repos/wildfire/trunk@6027 b35dd754-fafc-0310-a699-88a17e54d16e

build/build.xml

@@ -978,6 +978,8 @@
 
     </target>
     <target name="plugin" description="build one plugin">
+        <mkdir dir="${plugin.dest.dir}"/>
+
         <delete dir="${plugin.dev.dest.dir}/${plugin}"/>
         <delete file="${plugin.dev.dest.dir}/${plugin}.jar"/>
         <delete file="${plugin.dest.dir}/${plugin}.jar"/>