Project update fails after renaming file

1. Create a new Qt GUI Application.
2. In Projects view, right-click a source or header file and select "Rename..." from the menu.
3. Type "test" and press "Enter" to rename it.
   This works fine. The file is being renamed and the pro-file is being updated.
4. In Projects view, right-click the same file again and select "Rename..." from the menu.
5. Type "TEST" and press "Enter" to rename it.
   You'll see an error message:
   
   The pro-file is not being updated.

Found by Squish test tst_rename_file.