Implement the SSH message type.

* src/Makefile.am: Add message* files.
* src/server-func.c (guile_ssh_server_set_message_callback_x)
  (guile_ssh_server_message_get, callback): New procedures.
* src/server.scm (ssh:server-set-message-callback!)
  (ssh:server-message-get): Export.
* src/message-func.c, src/message-func.h, src/message-main.c,
  src/message-type.c, src/message-type.h, src/message.scm: New
  files.
Remove "ssh:" prefix from functions names.

* src/auth.c, src/auth.scm, src/channel-func.c,
  src/channel-type.c, src/channel.scm, src/key-func.c,
  src/key-type.c, src/key.scm, src/session-func.c,
  src/session-type.c, src/session.scm, src/version.c,
  src/version.scm: Remove "ssh:" prefix from functions names.
  Update comments.
src/session-func.c: Don't use the TYPE macro.

* src/session-func.c (session_options): Don't use TYPE macro to
  get names of SSH constants.
  (set_option): Likewise.
  (TYPE): Remove the macro.
NEWS: Update.
Merge branch 'master' into ssh-server-api

Conflicts:
	ChangeLog