Merge max-pending-computers-message [f=1662530] [r=chad.smith,landscape-builder,free.ekanayaka] [a=Alberto Donato]
This adds support in the client to handle a new error condition when trying to register a client, when there are too many pending computers already.
To do that, the client API version has been bumped, since the server needs to know if the client knows about this new error code.