Raise ActiveResource::ConnectionRefusedError on Errno::ECONNREFUSED

[balvig]

What

Raises a custom ActiveResource::ConnectionError when failing to connect to an external endpoint completely, changing something like:

Errno::ECONNREFUSED: Failed to open TCP connection to 127.0.0.1:4568 (Connection refused - connect(2) for "127.0.0.1" port 4568)

...into:

ActiveResource::ConnectionRefusedError: Failed to open TCP connection to 127.0.0.1:4568 (Connection refused - connect(2) for "127.0.0.1" port 4568)

Why

Follows the convention of rescuing network errors and wrapping them in ActiveResource custom errors, allowing them to be rescued without leaking knowledge of internals.