Rework the way IDF's SCM interface provides downloadable snapshots.

Instead of returning a command which gets executed and which should
pass through / stream its output data to the client, we're just
returning an instance of Pluf_HTTP_Response. This is needed, because
some SCMs, most noticable monotone, have no locally executable command
to provide a snapshot archive (and probably never will for our kind
of setup).

We therefor added a little BSD-licensed class "ZipArchive" which allows
the creation of pkzip-compatible archives on the fly by letting it eat
the file contents directly feed from the (remote) stdio instance.
Download performance is ok and lies between 15K/s and 110K/s, but at
least we do no longer block the browser while we pre-generate the zip
file server-side.

Thanks to Patrick Georgi for all his work!

contrib/zipstream-php-0.2.2/test/index.php

@@ -0,0 +1,52 @@
+<?php
+
+# load zipstream class
+require '../zipstream.php';
+
+# get path to current file
+$pwd = dirname(__FILE__);
+
+# add some random files
+$files = array(
+  '../extras/zip-appnote-6.3.1-20070411.txt',
+  '../zipstream.php',
+);
+
+# create new zip stream object
+$zip = new ZipStream('test.zip', array(
+  'comment' => 'this is a zip file comment.  hello?'
+));
+
+# common file options
+$file_opt = array(
+  # file creation time (2 hours ago)
+  'time'    => time() - 2 * 3600,
+
+  # file comment
+  'comment' => 'this is a file comment. hi!',
+);
+
+# add files under folder 'asdf'
+foreach ($files as $file) {
+  # build absolute path and get file data
+  $path = ($file[0] == '/') ? $file : "$pwd/$file";
+  $data = file_get_contents($path);
+
+  # add file to archive
+  $zip->add_file('asdf/' . basename($file), $data, $file_opt);
+}
+
+# add same files again wihtout a folder
+foreach ($files as $file) {
+  # build absolute path and get file data
+  $path = ($file[0] == '/') ? $file : "$pwd/$file";
+  $data = file_get_contents($path);
+
+  # add file to archive
+  $zip->add_file(basename($file), $data, $file_opt);
+}
+
+# finish archive
+$zip->finish();
+
+?>