+  oracle enhancements in test/coloring

that is now genarated all the times by rdbg

Of course this is only useful for algo that compute some kind of trees (more
specifically, this only work if the state contains a variable named "par" !)

Add use it to add an oracle to the BFS

Fix: take into account in dot.ml the change in Topology done in #e76aa9be

where a weigth label has been added

This is necessary because I cannot Dynlink .cmxs files from a ocaml
toplevel. Hence, one way to load the algos from rdbg is to
#load .cma files. This option generates an ocaml file that
can be #used by automatically generated rdbg-session.ml files.

Depending on the kind of network, we should raise an exception. Indeed
such information should not be available in anonymous networks.

We will add such checks later.

instead of duplicating its content