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.

Squashed commit of the following:

commit 390841c31c900117ee1bcd96fdb685abc67640ba
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 15:00:25 2011 +0200

    Separated SSL test server.

commit 71293ace2e87ba0a7d58261ac37ce203d1660da5
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 14:57:58 2011 +0200

    SSL auth shall not be used for download.

commit 9c9decdf247b13b46b1d00977b06060af668ad24
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 14:45:01 2011 +0200

    Skip some tests.

commit 8ef48e73192e44563ba21358ab684419d4fc8b70
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 10:26:59 2011 +0200

    PEP8ised.

commit 260e0951d724be3f81df25ef7f9fce5d8922be89
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 10:25:35 2011 +0200

    Implement tests.

commit 8900f71910210e14d5af92189bb1ab92fb75c069
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Wed Aug 31 10:22:18 2011 +0200

    Implement ssl based tests.

    Unfortunately no internal SSL server with authentication is available.

commit e1818af334ee572838a04d384f5088fef9b9af7f
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 15:56:17 2011 +0200

    Provide authnetication SSL keys.

    Also import some CA certificte which validates them.

commit 8b5ee8652975b252623c19be5416812b22bf916c
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 15:39:12 2011 +0200

    Mark tests to be implemented.

commit ebce98a58171d90008bd172036642cb04c00ffa8
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 15:37:36 2011 +0200

    Test that auth key and cert are accepted.

    Assertion simplified to checking that they are set.

commit 1dc200d15a09d91366962b0d248191d4289304cc
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 15:34:00 2011 +0200

    Share key and certificate between tests.

commit eb870df4ed55c595519843c32103ca5d3b9fe24a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 15:30:22 2011 +0200

    Implement SSL based authentication.

    Accept key and certificate and pass them in case of using https scheme while
    putting content to shacache and shadir.

commit ac219f335e687659a2e28719044d7c8267d1dfce
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 14:21:24 2011 +0200

    Expose authentication parameters.

commit 1b960b07504a390cc1ecdfd598f4148753176447
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 14:19:45 2011 +0200

    Describe parameters.

commit 2a0186478a5c699ac77fa526f31b5a5a92069f72
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Aug 30 14:17:27 2011 +0200

    Reformat parameter list.

Except list of PEM encoded certificate strings. Do not try to read them from
file nor download from network.

Also fix few naming errors.

Compat: Put key as first argument.

Spec: In case of passing key (and updating shadir) require urlmd5 too.

Key is given by the library user. It has no internal meaning.

Note: Soon the best *one* module will be selected.

Required parameters are:

 * file: the name of the file
 * urlmd5: mdsum of orginal url
 * sha512: the hash (sha512) of the file content

Optional ones:

 * valid-until: the date which the file must be expired
 * architecture: computer architecture