evolve: make `--continue` continue evolving all remaining revisions This patch makes `hg evolve --continue` to continue all remaining revisions instead of just the current conflicted one. There are some still improvements required to this behavior after which the CHANGELOG entry will be added.

tests: add more tests to test-evolve-continue.t This patch adds more tests for `hg evolve --continue`. The tests demonstrates how the continuation handling of hg evolve is broken and the later patches fixes that handling.