doc/guile-ssh.texi (Installation): Update

* doc/guile-ssh.texi (Installation): Update URLs to Guile-SSH
  repository.  Require libssh 0.6.3.
* NEWS: Update.
ssh/channel-type.c (print_channel): Use `SCM_OPPORTP' predicate
tests/client-server.scm (spawn-server-thread): Catch all exceptions

* tests/client-server.scm (spawn-server-thread): Catch all exceptions
  to fix the "Error while printing of exception" during the tests.
* tests/server-client.scm (spawn-client-thread): Likewise.
Merge branch 'master' into gc-bug-fix