Support Domain module

The attached file has the function necessary to implement domain_conf's hook that will allow multiple API keys on a site that uses the Domain Access module.

The code works, but the file doesn't, not sure why... It's the first time I've added code to an existing module, so all it needs is someone that knows what they're doing to fix whatever little mistake I made.

After that, just add the file to the GMap module directory and multiple Google Map API keys are enabled.