rdesktop patch to add limited RDPv6 + CredSSP

I have recently finished a project that adds support for limited aspects of RDPv6 to rdesktop. Specifically I have added support for SSL and SSL + CredSSP. These are the protocols that must be used when "High Security" or "Network Level Authentication" is enabled on the server side. The patch has been tested against Server 2008, 2008R2 and Windows 7 and both scenarios are working well.

A few notes:

• These diffs were generated from rdesktop SVN revision 1600.
• CredSSP allows for Kerberos as well as NTLM authentication. This enhancement supports NTLMv2 only.
• Where NTLMv2 is concerned, I tried to use the Heimdal NTLM library however I could not make this work. After going around for a while with Microsoft support, I came to suspect Heimdal's NTLMv2 implementation. The best alternate implementation of NTLMSSP that I could find is buried in Samba. Unfortunately, Samba does not produce externally useful shared libraries as part of its build. So, if you wish to enable CredSSP (not required for mere SSL but it is required for NLA) then you'll have to download and build Samba3 from source before you rebuild rdesktop. I used samba-3.5.5, configured with --without-winbind and then built normally. Reconfigure rdesktop, adding --with-samba= to your configure command line. With this option the rdesktop link will pull in 3-4 extra static libraries from the samba build. Thus there is no runtime dependency on Samba, only a built-time dependency. This is unfortunate and if someone could produce a better standalone NTLMSSP implementation that would obviously be a great improvement.
• No other aspects of RDPv6+ were added.
• This has been tested with Ubuntu 10.04.1 and Cygwin.

We hope these are useful to the community and can help to jump-start RDPv6 support in the rdesktop trunk.

- David Joyner