debugrevlog: fix computing chain length in debugrevlog -d The chain length was computed correctly only when generaldelta feature was enabled. Now it's fixed. When generaldelta is disabled the base revision in revlog index is not the revision we have delta against - it's always previous revision. Instead of incorrect chainbaseandlen in command.py we are now using two single-responsibility functions in revlog.py: - chainbase(rev) - chainlen(rev) Only chainlen(rev) was missing so it was written to mimic the way the chain of deltas is actually found during file reconstruction.