Add nordugrid-arc 2.0.0 formula

The Advanced Resource Connector (ARC) middleware integrates computing
resources (usually, computing clusters managed by a batch system or
standalone workstations) and storage facilities, making them available
via a secure common Grid layer.

The formula also provides the client tools required to use ARC resources.

Depends on https://github.com/mxcl/homebrew/pull/15271