Improve temp file name, props DD32, fixes #10224

git-svn-id: https://develop.svn.wordpress.org/trunk@11712 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/includes/file.php

@@ -171,6 +171,7 @@ function wp_tempnam($filename = '', $dir = ''){
 	if ( empty($filename) )
 		$filename = time();
 
+	$filename = preg_replace('|\..*$|', '.tmp', $filename);
 	$filename = $dir . wp_unique_filename($dir, $filename);
 	touch($filename);
 	return $filename;