[RFC] support for encrypted documents v1

[Michal H. <ms...@gm...>]

Attached patchset enables read-only access to encrypted documents.
Detailed patch description will come in reply to this email. Please
review all patches and give me feedback. I have tested it with some
encrypted documents (attached one in bug 195 and some exported from open
office).
Patch is against current trunk.
-- 
Michal Hocko