Edited Issue: No indication when debuggee rejects attach because something else is already attached [779]

When attaching to a node.exe process that already has the debugger attached, it's going to reply with the corresponding error message as its first response packet, and then shut down the connection. However, we don't handle this in any special way, either when enumerating processes in Attach to Process dialog, nor when actually attaching. So in the Attach to Process dialog, the process will actually show up as valid, and when doing the actual attach, VS will show up as attached and then detach immediately due to connection breaking.

We need to watch out for that debugger response, and provide the appropriate indication to the user.