Previously just empty strings were signed and verified.

Squashed commit of the following:

commit b3e1bf51989599a136f2a42f63688aa3048aae12
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 15:59:40 2011 +0200

    Really sign the content.

commit c4a6abd652f7ca19fad66188ec7c782956392b68
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 15:59:07 2011 +0200

    Show that hacked content is not trusted.

commit 08340918639598b227dd346d4ab6054428296d60
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 15:12:09 2011 +0200

    Positive test of signed content.

commit a00a2a5b788542d324561d4d6418b86c1cb9f86d
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 15:00:54 2011 +0200

    Skip if no standalone server is available.

commit f31ef55187c46305b2ae8034ee496cc28af12893
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 14:32:39 2011 +0200

    Move offline tests to one place.

    Remove non sense tests.

commit d725dcd24b95f5bbbb340a6fe6ce5ea7f8aed4d5
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 14:14:34 2011 +0200

    Start to really sign the content.

    Previously empty strings were signed and verified.