Make a class graph of the type displayed by the Tycho EditDAG class.
The first argument is the name of the graph. The second argument is
the name of the graph file to create. The rest of the arguments are
any number of file names from which the graph should be created.
If any of these files is not readable, it is ignored.
These file names should be absolute (or relative to an environment
variable like TYCHO) so that the resulting hyperlinks work from any
directory. To create a graph for the entire Tycho tree, use the
procedure tychoStandardClasses
.
We could have tydoc generate this information, but it would be much slower.