Incremental packaging.

src/main/kotlin/com/beust/kobalt/plugin/packaging/PackagingPlugin.kt

@@ -61,19 +61,12 @@ class PackagingPlugin @Inject constructor(val dependencyManager : DependencyMana
                 runTask = { taskInstall(project) })
     }
 
-    /**
-     * "assemble" is an incremental task but with a twist. Because it can be costly to determine if any
-     * of the class files generated in the previous phase is new or not, we just don't do that and always
-     * return "null" for both input and output checksums, which would cause that task to always be rerun.
-     * However, we are depending on Kobalt's cascading incremental management to skip us whenever appropriate:
-     * whenever a previous incremental task was a success, all following incremental tasks are automatically
-     * skipped.
-     */
     override fun assemble(project: Project, context: KobaltContext) : IncrementalTaskInfo {
         val allConfigs = packages.filter { it.project.name == project.name }
 
-        if (false) {
-            // Work in progress
+        val start = System.currentTimeMillis()
+        val checksums =
+            if (true) {
                 val allIncludedFiles = arrayListOf<IncludedFile>()
                 val zipToFiles = hashMapOf<String, List<IncludedFile>>()
                 val outputArchives = arrayListOf<File>()
@@ -99,14 +92,21 @@ class PackagingPlugin @Inject constructor(val dependencyManager : DependencyMana
                     files
                 }
 
-            val md5 = Md5.toMd5Directories(allFiles)
+                val inMd5 = Md5.toMd5Directories(allFiles)
                 val outMd5 = Md5.toMd5Directories(outputArchives)
-            println("Input MD5: $md5 output MD5: $outMd5")
+                Pair(inMd5, outMd5)
+            } else {
+                Pair(null, null)
             }
 
+        val inMd5 = checksums.first
+        val outMd5 = checksums.second
+        context.logger.log(project.name, 2,
+                "    Time to calculate packaging checksum: " + (System.currentTimeMillis() - start) + " ms")
+
         return IncrementalTaskInfo(
-                { null },
-                { null },
+                { -> inMd5 },
+                { -> outMd5 },
                 { project ->
                     try {
                         project.projectProperties.put(Archives.JAR_NAME,