Check upload_tmp_dir ini settings for a usable temporary path. Props Denis-de-Bernardy. fixes #6699

git-svn-id: https://develop.svn.wordpress.org/trunk@12519 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/includes/file.php

@@ -155,6 +155,10 @@ function get_temp_dir() {
 
 	if  ( function_exists('sys_get_temp_dir') )
 		return trailingslashit(sys_get_temp_dir());
+	
+	$temp = ini_get('upload_tmp_dir');
+	if ( is_dir($temp) ) // always writable
+		return trailingslashit($temp);
 
 	return '/tmp/';
 }