Fotmatting: in `sanitize_file_name()`, escape `%` when uploads contain them, otherwise attachment URLs will unescape the char and break.

Adds unit tests.

Props mordauk, simonwheatley, dd32, solarissmoke.
Fixes #16226.

Built from https://develop.svn.wordpress.org/trunk@35122


git-svn-id: http://core.svn.wordpress.org/trunk@35087 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/formatting.php

@@ -1368,7 +1368,7 @@ function remove_accents( $string ) {
  */
 function sanitize_file_name( $filename ) {
 	$filename_raw = $filename;
-	$special_chars = array("?", "[", "]", "/", "\\", "=", "<", ">", ":", ";", ",", "'", "\"", "&", "$", "#", "*", "(", ")", "|", "~", "`", "!", "{", "}", chr(0));
+	$special_chars = array("?", "[", "]", "/", "\\", "=", "<", ">", ":", ";", ",", "'", "\"", "&", "$", "#", "*", "(", ")", "|", "~", "`", "!", "{", "}", "%", "+", chr(0));
 	/**
 	 * Filter the list of characters to remove from a filename.
 	 *

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-35121';
+$wp_version = '4.4-alpha-35122';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.