Issue #2745013: drupal_random_key() documentation for length of returned string is wrong

Closes #2745013

includes/bootstrap.inc

@@ -2285,7 +2285,8 @@ function drupal_block_denied($ip) {
  *   The number of random bytes to fetch and base64 encode.
  *
  * @return string
- *   The base64 encoded result will have a length of up to 4 * $byte_count.
+ *   A base-64 encoded string, with + replaced with -, / with _ and any =
+ *   padding characters removed.
  */
 function drupal_random_key($byte_count = 32) {
   return drupal_base64_encode(drupal_random_bytes($byte_count));