Check editor accounts.

A new editor needs a username and a password of at least 12 characters. A persistent login needs an unexpired key and an existing account. Removing an account revokes its persistent logins, and its sessions end.

open_db.lib.php

@@ -36,6 +36,22 @@ function open_db($state) {
   }
 }
 
+/*
+ * TRUE if an editor account named $username exists. A session or a
+ * persistent login of an editor whose account was removed ends with it.
+ */
+function editor_exists($username) {
+  global $db;
+  if (!is_string($username) || $username === '')
+    return FALSE;
+  $opened = open_db('open');
+  $result = $db->execute_query("SELECT username FROM editors WHERE username = ?", array($username)) or db_fail();
+  $row = $result->fetch_assoc();
+  if ($opened)
+    open_db('close');
+  return (bool)$row;
+}
+
 /*
  * Stop the page after a database error. The details, with the file and
  * line of the failed call, go to the PHP error log; the visitor only