changing label of files with same name changes both labels

If you have attach two files with the same name, but different paths, and change the label in one, apon reopening the project, both files have the same label. To reproduce:

1) Add test1/image01.jpg to project
2) Add test2/image01.jpg to project

Change label of first image01.jpg. After saving project, and closing openshot and reopening project, both files have same label. This occurs in version 1.3.0, and latest from trunk. Running archlinux (latest, rolling release).

This occurs because the UpdateFileLabel function works on the "name" of the file object. Changing this to use the file objects unique_id fixes this problem. I've attached a bzr send -o of the changes i did to fix this problem. I've also removed references to UpdateFileLabel from the TreeHistory, TreeBlender, and TreeEffects classes, as the cell_edited function is never called in these classes as none of the forms cells are editable.

I've never used bzr before, so not sure if the bzr send -o command is the right one to use in this circumstance, but its output is text based so you can get the patches from the merge file at any rate.