Rename package jet -> kotlin in ant

org.jetbrains.jet.buildtools.ant -> org.jetbrains.kotlin.ant

The old antlib.xml is kept for migration purposes

compiler/testData/integration/ant/js/simpleWithMain/build.xml

@@ -1,5 +1,5 @@
 <project name="Ant Task Test" default="build">
-  <taskdef resource="org/jetbrains/jet/buildtools/ant/antlib.xml" classpath="${kotlin.lib}/kotlin-ant.jar"/>
+  <taskdef resource="org/jetbrains/kotlin/ant/antlib.xml" classpath="${kotlin.lib}/kotlin-ant.jar"/>
 
   <target name="build">
     <kotlin2js src="${test.data}/root1" output="${temp}/out.js" noStdlib="true" main="call"/>