Removed in_request_pty_exec and in_subsystem flags, and removed uses of MASK_SHELL in bitmap, replacing with open channel status queries.
Adding channel argument to read, write, and reset allowing callers to select among multiple open interactive channels.
Adding interactive channel identifier interface as sanctioned path for users to obtain channels ids instead of using channel constants.
Deprecating get_interactive_channel helper and documenting its "legacy" behavior in read, write, and reset doc blocks.
Removing disconnect on timeout in channel close for lack of clarity around timeout origin.
Check for open channel prior to closing in stopSubsystem and reset.
