The sollution of Russel works if you leave the .mendix-cache and the .svn directories intact. So delete all the other files and copy the files (without those hidden directories) from your other project to this directory and do a commit. Since you have kept those hidden directories the changes will be picked up by the modeler.
Any reason why you didnt just make a copy of the oringial project as a backup and then just upgrade the existing project within its own folder? That would have been the cleanest way to handle that.