Consolidate/Export tracks - behave like Render when files exist

[killergege]

Make the Consolidate/Export tracks screen behave like the render screen : if the files already exist it should display a "render warning" screen with a "Files already exist" message and "Increment filenames" & "Overwrite" buttons.
Today it increments the filenames without warning nor giving an overwrite option.

I use Consolidate to export comped tracks for mixing in another session, and it's a bit annoying to have to clean the folder or rename the files.