rgraph: Improve error rgraph traversal
rgraph: Improve error rgraph traversal

Yields tuples (reason, shift) in the reverse order. which is chosen
in order to make output examination more natural to users.
This method is most useful in case of shortened rgraph.

See traverse_error_graph docs for details

abusalimov/mybuild,abusalimov/mybuild,embox/mybuild,embox/mybuild