ssh/channel.scm: Don't export primitive procedures

* ssh/channel.scm (%channel-open-forward)
  (%channel-open-forward/reverse): Don't export primitive procedures.
* doc/api-channels.texi (Channels): Update.
* NEWS: Update.
.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 port-forwarding

Conflicts:
	ChangeLog
	NEWS