doc/threat.html: contacts learn about revocations
Support merged acks.

ACKs can now be merged with other, pending messages to the same contact.
(Including other ACKs themselves.)
Merge branch 'leif-threat-model'
Allow server to return several revocations at once.

If there is more than one revocation pending for a contact, the server
will now return as many revoctaions as will fit in the error message.
Merge branch 'duy-master'
added server cl option to disable registration of new accounts
Two CLI fixes.

1) After the change to late signing, a typo meant that the client would
   exit when sending a message.

2) Drafts created in the UI don't always have a destination contact set
   so a statefile that was used in both the GUI and CLI could end up
   crashing the UI.

Time to start writing unittests of the CLI as well as the GUI.
Move --disable-registration to config and add error code.
Merge branch 'duy-disablereg'
Prompt twice for passphrases in the CLI.
Support erasure storage for statefiles created via the CLI.
Add RUNNING documentation.
Update paper draft.

(Second draft, it needs a lot of work.)
Add Pond server setup documentation
Go 1.0 needs return statements.
cli.go uses the TPM-related message strings.

Needed when building with -tags nogui.
Update to account for changes in the ed25519 package.
Merge branch 'ln5-fixes'
Fixes to the "running a server" documentation.
Merge branch 'david415-david-server-setup-docs'