Do not allow modules to be enabled at all if they have conflicting config file names with any existing config.

https://github.com/backdrop/backdrop-issues/issues/1238#issuecomment-141...

When the module is enabled backdrop would check that there is no naming issues, warn of any path issues and copy these files into the sites config folder.

I think this would be a good idea in any case. We shouldn't allow modules to be enabled at all if they have conflicting config file names with any existing config.