discovery: introduce "stable slicing" methods We introduce new code that leverage the stable sorting to slices a graph in a way "stable" accross repository. This should allow us to use theses slices for obsolescence markers discovery.

discovery: adds a function doing revnum independant sorting The function is doing a topological sort without depending on revision number. This make the sort independent of the repository and suitable for discovery.

hgignore: also ignore the 'dist' directory This is generated by the 'sdist' command