obslog: uniformize `_debugobshistoryrevs` and `_debugobshistorygraph` arguments `_debugobshistoryrevs` and `_debugobshistorygraph` perform quite the same action, the latter simply add graph support. Consequently, it looks better for them to have the same argument list.

obslog: fix --patch with --no-graph options The repo given to _debughistorydisplaymarker which computes the diff was filtered when graph mode is disabled.