Filesystem API: Prevent an endless self-calling loop in `wp_tempnam()`.

Under certain conditions upgrades on Windows may fail because `wp_tempnam()` gets called in a loop.
This can happen when `wp_tempnam()` is called with `\.maintenance` for the `$filename` parameter. The function strips the extension, in this case `.maintenance`, which results in an empty filename. Because it's empty, `wp_tempnam()` calls itself with `dirname( '\.maintenance' )`. On *nix systems this would be `"/"` which allows `wp_tempnam()` to fall back on `time()`. But on Windows it's `"\"`.

This change adds the backslash to the list of characters which allow `wp_tempnam()` to fall back on `time()`.

See [32322], [31936].
Fixes #33999.
Built from https://develop.svn.wordpress.org/trunk@38151


git-svn-id: http://core.svn.wordpress.org/trunk@38092 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/file.php

@@ -168,7 +168,7 @@ function wp_tempnam( $filename = '', $dir = '' ) {
 		$dir = get_temp_dir();
 	}
 
-	if ( empty( $filename ) || '.' == $filename || '/' == $filename ) {
+	if ( empty( $filename ) || '.' == $filename || '/' == $filename || '\\' == $filename ) {
 		$filename = time();
 	}
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-beta4-38150';
+$wp_version = '4.6-beta4-38151';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.