Rework tracing support

I was slightly unhappy with it:
 * dylan-compiler required network and serialization library
 * filtering was implemented in a bad way
 * it modified way too much of compiler internals

Now, the interface is not via an external TCP/IP socket, but I rather importing the dfmc-flow-graph library and setting the value of *trace-dfm-callback* and other variables; which also provides a unified filter.