[boost] [graph] improvements on/documentation for transitive_reduction.hpp

Hi there! I did improve on the transitive reduction and wrote some documentation. As there are multiple files now, I did not send them to the mailing list. Shall I send a tar.gz to the mailing list? How can I contribute these files to the graph library? As I wrote the code/documentation I noticed that it is possible to implement the transitive reduction by a few minor changes to the existing transitive_closure algorithm (and it would be better). I will follow that path someday in the future. Yours sincerely, Eric Böse-Wolf