wireprotoserver: identify requests via version 2 of SSH protocol as such The protocol handler needs to advertise itself as version 2 in order for a future feature to work. Differential Revision: https://phab.mercurial-scm.org/D2484

wireproto: allow wire protocol commands to declare transport support Currently, wire protocol commands are exposed on all transports. Some wire protocol commands are only supported or sensical on some transports. In the future, new wire protocol commands may only be available on new transports and legacy wire protocol commands may not be available to newer transports. This commit introduces a mechanism to allow @wireprotocommand to declare transports for which they should not be available. The mechanism for determining if a wire protocol command is available for a given transport instance has been taught to take this knowledge into account. To help implement this feature, we add a dict to wireprototypes declaring all wire transports and their metadata. There's probably room to refactor the constants used to identify the wire protocols. But that can be in another commit. Differential Revision: https://phab.mercurial-scm.org/D2483