unix-socket removed

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

Just a heads up: v0.2 will also have the unix-socket backend broken when I 
merge into master. 

Part of the breakup of the repository means that we can use the standard Lwt 
UNIX module to access kernel sockets, and no longer need our shim layer.  
Switching to upstream Lwt pulls in numerous bug fixes (particularly in the 
libev integration, which is a bit tricky with respect to the garbage collector 
and generational roots).

But in the very short term, only unix-direct and xen-direct will work.  I'm 
thinking the TCP stack is in good enough shape to just turn the default live 
openmirage.org to use the microkernel version now; who needs UNIX sockets eh!

-anil