Those helpers cover most of slapgrid use cases: download AND upload from/to
string (fd), file, directory.

Fetch all trustable entries and let client decide which entries to use.

This reverts commit 2a9024fc.

This reverts commit 5ed93f4c.

Squashed commit of the following:

commit 5c74964a312fb743f88a115ffb4d5af44dd3d2d1
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Fri Sep 2 10:22:48 2011 +0200

    No more M2Crypto is required.

commit 71ddc285850bd1c5761b95cff8616c6023f6eadf
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Fri Sep 2 10:22:03 2011 +0200

    Drop M2Crypto dependency.

    Simplify, generate only common name in key.

commit 9e058070bc66fc91a590d90adf379a899b00d124
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 18:05:14 2011 +0200

    Cover cases when openssl is not compatible.

    It seems that python executable can be seen as openssl begin not compatible.

commit 69901f159392db65597b97482439bea4d002e9c4
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 18:00:27 2011 +0200

    Raise correctly in case of openssl unavailabilty during upload.

    More: raise DirectoryNotFound in more cases.

commit c17c46053385b586e7ccdb4ebf3ecb9ab46d901b
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 18:00:08 2011 +0200

    Cover case when no openssl is available during upload.

commit d88d9e2b892000fa64c28b74182777fd03c93556
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:55:23 2011 +0200

    Covert case when empty shadir entry is in shadir.

commit 6671546db794a5ea8e7025de115a613940e4af14
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:45:08 2011 +0200

    Add no openssl during content selection test.

    Add another test skeleton.

commit ad6b3b5abbbb2d8267938661946acf1bd4d02b43
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:32:09 2011 +0200

    Close another temporary file.

commit 34d15b585e52810908323cf846af5a64171f62b2
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:23:23 2011 +0200

    Expose openssl and avoid dying in case if not exists.

commit 0eb456fc6ccd2d36644c47abc1ef79b7b51187c6
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:15:54 2011 +0200

    Pep8isation.

commit 7179acf759a1d18bff367025a965d020443f93e2
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 1 17:12:25 2011 +0200

    Drop M2Crypto dependency.

    M2Crypto is unmantained library. It seems safer to use openssl directly to
    sign and verify content.

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.