CommitService.FindCommits: disabling `follow` for Git Range Notations
Git range revspecs have the potential to be as much harmful with the `follow` option than the redundant ancestors iteration we already removed for #117, but it will take us more time to find out how to treat them efficiently. Meanwhile, we prefer to fall back to ignoring copy-tracing rather than risking it to crash the entire system. In Git world, copy-tracing is a best-effort anyway (heuristic with several levels of analysis) This finishes the work on this nasty resource exhaustion issue. Closes #117