Reorganize test suite.

- Split testLoginLogout() into testBadLogin() and testLoginLogout().
- Mark testCreateSimpleArticle() as incomplete until the popup
  window opened by clicking on VIEW is handled correctly.
- Disable mod_rewrite so that the test suite does not depend on it.
- Remove superfluous check for Testing_Selenium class.
- Migrate TestConfiguration.php.dist to config.xml.dist.
  - Configure whitelist for code coverage information.
    - Be conservative for now and only add include/ and plugins/
      directories for now.
    - Set addUncoveredFilesFromWhitelist="false" because not all
      files are loadable (yet).
- Add documentation for code coverage reporting.

tests/coverage/append.php

@@ -0,0 +1,20 @@
+<?php
+if ( isset($_COOKIE['PHPUNIT_SELENIUM_TEST_ID']) &&
+    !isset($_GET['PHPUNIT_SELENIUM_TEST_ID']) &&
+    extension_loaded('xdebug')) {
+    $GLOBALS['PHPUNIT_FILTERED_FILES'][] = __FILE__;
+
+    $data = xdebug_get_code_coverage();
+    xdebug_stop_code_coverage();
+
+    foreach ($GLOBALS['PHPUNIT_FILTERED_FILES'] as $file) {
+        unset($data[$file]);
+    }
+
+    file_put_contents(
+      $_SERVER['SCRIPT_FILENAME'] . '.phpunit_' .
+      $_COOKIE['PHPUNIT_SELENIUM_TEST_ID'],
+      var_export($data, TRUE)
+    );
+}
+?>