Revert changes to ZipArchive

ZipArchive comes from scalac but was modified because the local class
failed to be pickled correctly previously. This appear to be fixed now,
so we can close scala#2340.

Author: smarter

compiler/src/dotty/tools/io/ZipArchive.scala

@@ -205,11 +205,12 @@ final class ManifestResources(val url: URL) extends ZipArchive(null) {
     for (zipEntry <- iter) {
       val dir = getDir(dirs, zipEntry)
       if (!zipEntry.isDirectory) {
-        val f = new Entry(zipEntry.getName) {
+        class FileEntry() extends Entry(zipEntry.getName) {
           override def lastModified = zipEntry.getTime()
           override def input        = resourceInputStream(path)
           override def sizeOption   = None
         }
+        val f = new FileEntry()
         dir.entries(f.name) = f
       }
     }