Update to 4.0.0.

Note that while the protocol is compatible, the API is not, and hence
there will be a pidgin-otr update within minutes.

There is an apparent gcc 4.1.3 -O2/SSP bug, which is avoided by
disabling SSP in libotr (which libotr finds and turns on).  This is
temporary pending more fine-grained control and/or a fix.

Update to libotr 4.0.0.  Note that libotr 4.x is API-incompatible with
libotr 3.x; upstream thinks this is ok, so pkgsrc won't try to work
around it.

24 Aug 2012:
- Release 4.0.0
- Support v3 of the OTR protocol
- The main new feature: sensibly handle the case where a user is logged
  in multiple times to the same IM account
- API changes:
  - instance tags, to support multiple simultaneous logins
  - support for asynchronous private key generation
  - the ability to provide an "extra" symmetric key to applications
    (with forward secrecy)
  - applications can supply a formation conversion callback if they do
    not natively use XHTML-style UTF8 markup
  - error messages formerly provided by libotr are now handled using
    callbacks to the application, for better i18n support
  - otrl_message_sending now handles message fragmentation internally

(gdt)