The commands involved are mark-conflict, pull, and apply.
When conflicts are reported, we just see a list of files where conflicts
occur. We could have more information to see how bad the situation is:
1) how many hunks are conflicting in each files
2) the kind of conflicts: add, move, delete, replace, etc.
The function Darcs.Patch.Summary plainSummaryPrims already gives us 2).
For 1), it gives the number of lines involved in the conflict markers.