Certificate signing stuff.

[hoverlover]

I cannot take much credit for this commit. Most of it was taken from @carnesmedia's Savon fork. I made one bug fix (DigestValue out of order) and the rest of the work I did was simply porting the changes over to Akami, since the original author's changes were based when Akami was still a part of Savon.

There are no specs for these changes. I feel bad about this, but there are two reasons:

1. @carnesmedia's fork did have specs, but they were written while it was part of Savon. These specs simply don't work under Akami due to missing classes from Savon, among other things.
2. I made these changes out of necessity for something I'm working on for a client, and am a little under the gun to get this up and running, so I didn't have the time to make the specs work under Akami. I know, lame excuse, but that's the truth.

I've tested these changes with some live requests, and it does work. If you don't want to accept the pull request without specs, it will at least serve to let others know about my fork if they need certificate signing in conjunction with Savon/Akami. I will hopefully have time in the near future to get the specs working and pushed.

[amiel]

BTW: I think Nokogiri has real canonicalization support now...

[hoverlover]

Great! I will look into that.