log: remove caching of all visited revisions (
issue3253)
Not only does this eat all available memory for some users, it's slower.
convert: use splicemap entries when sorting revisions (
issue1748)
When sorting revisions before converting them, we have to edit the revision
graph using splicemap entries. Otherwise, a spliced revision may be converted
before its synthetic parents. Invalid splicemap revisions are now detected
before starting the conversion.