Silence warning when compiling without XML.
Moving documentation in .c files from header files.

This is documentation the programmer has to see the moment he looks up
the function name, and currently most (all?) editors take you to the
implementation, not the declaration.
TODO
cleanups
More cleanups.
body common control: protocol_version
Tests ok.
Define CF_PROTOCOL_LATEST same as CF_PROTOCOL_TLS.

Also make the code a bit more future-proof, if more than one protocols
ever exist inside the TLS layer.