Add PHP unit tests and page tests.

Run "composer install", then "composer test".

tests/php/Support/Mail.php

@@ -0,0 +1,41 @@
+<?php
+namespace Xxx\Tests\Support;
+
+/*
+ * Mail sent by code in a subprocess. PHP reads sendmail_path only at
+ * start-up, so code that sends mail runs in a new PHP process with
+ * tests/php/fixtures/fake-sendmail.php as its sendmail.
+ */
+class Mail {
+  /*
+   * PhpProcess::run() with the fake sendmail. The result has an extra
+   * 'mails' entry: a list of array('headers' => name => value,
+   * 'subject' => ..., 'body' => ...), decoded.
+   */
+  public static function run(string $code, array $env = array(), array $ini = array()): array {
+    $log = tempnam(sys_get_temp_dir(), 'xxx-mail-');
+    $sendmail = escapeshellarg(PHP_BINARY) . ' ' . escapeshellarg(XXX_ROOT . '/tests/php/fixtures/fake-sendmail.php');
+    $result = PhpProcess::run($code, array('MAIL_LOG' => $log) + $env, array('sendmail_path' => $sendmail) + $ini);
+    $result['mails'] = array();
+    foreach (file($log, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES) as $line)
+      $result['mails'][] = self::parse(json_decode($line, TRUE)['message']);
+    unlink($log);
+    return $result;
+  }
+
+  public static function parse(string $message): array {
+    list($head, $body) = preg_split('/\r?\n\r?\n/', $message, 2) + array('', '');
+    $headers = array();
+    foreach (preg_split('/\r?\n(?![ \t])/', $head) as $line) {
+      list($name, $value) = explode(':', $line, 2) + array('', '');
+      $headers[strtolower(trim($name))] = trim(preg_replace('/\r?\n[ \t]+/', ' ', $value));
+    }
+    $encoding = strtolower($headers['content-transfer-encoding'] ?? '');
+    if ($encoding === 'base64')
+      $body = base64_decode($body);
+    else if ($encoding === 'quoted-printable')
+      $body = quoted_printable_decode($body);
+    return array('headers' => $headers, 'subject' => mb_decode_mimeheader($headers['subject'] ?? ''),
+                 'body' => str_replace("\r\n", "\n", $body));
+  }
+}