[BioC] Rgraphviz: read .dot file

[Vincent Carey 525-2265]

> In RGraphviz or graph, there is no function to read a .dot file to create a graph object for use in Rgaphviz or I am missing something? Thanks.
>

we are improving the handling of dot files.  at the moment,
you can use dot2gxl (a utility provided with graphviz, not Rgraphviz)
to transform dot to XML, then use the fromGXL method
of the graph package.

not all attributes expressible in dot or GXL will be
propagated to the graph -- let us know if some key attributes
need to be added for propagation.