ssh/message-func.c: Fix warnings

* ssh/message-func.c (get_auth_req, get_pty_req, get_env_req)
  (get_exec_req, get_global_req, get_service_req, get_channel_open_req):
  Fix warnings: Add `const' qualifier where it is needed.
ssh/message-func.c (get_auth_req): Fix a bug

* ssh/message-func.c (get_auth_req): Fix a bug with assignment of
  `ssh_public_key' type to `ssh_key' variable: Use
  `ssh_message_auth_pubkey' instead of `ssh_message_auth_publickey' to
  get the key.
.dir-locals.el: Add to the repository
doc/guile-ssh.texi: Improve the "Examples" chapter

* doc/guile-ssh.texi: Add an overview of programming with Guile-SSH to
  the "Examples" chapter.
* doc/examples.texi: Add to the repository.
* doc/Makefile.am (guile_ssh_TEXINFOS): Add `examples.texi'.
* doc/version.texi: Update.
* NEWS: Update.
tests/client-server.scm: Add TCs for `authenticate-server'

* tests/client-server.scm ("authenticate-server, not-known")
  ("authenticate-server, ok"): New TCs.
* NEWS: Update.
Merge branch 'master' into gc-bug-fix