A new RPC pipe! The \pipe\echo named pipe is for testing large RPC

A new RPC pipe!  The \pipe\echo named pipe is for testing large RPC
requests and responses and is only compiled in when --enable-developer
is passed to configure.  It includes server and client side code for
generating and responding to functions on this pipe.  The functions are:

 - AddOne: add one to the uint32 argument and return ig
 - EchoData: echo back a variable sized char array to the caller
 - SourceData: request a variable sized char array
 - SinkData: send a variable sized char array and throw it away

There's a win32 implementation of the client and server in the
junkcode CVS repository in the rpcecho-win32 subdirectory.