graft: fix collision detection with origin revisions that are missing...
graft: fix collision detection with origin revisions that are missing
When grafting something with a matching origin, it would normally be skipped:
skipping already grafted revision 123 (23 also has origin 12)
But after stripping a graft origin, graft could fail with a reference to the
origin that no longer exists:
abort: unknown revision '5c095ad7e90f871700f02dd1fa5012cb4498a2d4'!
Instead, detect that the origin is unknown and skip it anyway, like:
skipping already grafted revision 8 (2 also has unknown origin 5c095ad7e90f871700f02dd1fa5012cb4498a2d4)
