ancestor: filter out initial revisions lower than stoprev

ancestor: add test showing inconsistency between __iter__ and __contains__

ancestors: ensure a consistent order even in the "inclusive" case It seems odds to first issue the "source" revs and then the other ancestors. In addition, doing so can break the other contract of always issuing a child before its parent. We update the code to apply the same logic to all yielded revision. No tests break so we seem in the clear except where we explicitly test the order.

ancestors: actually iterate over ancestors in topological order (issue5979) This code previously used a dequeue logic, the first ancestors seen were the first ancestors to be emitted. In branching/merging situations, it can result in ancestors being yielded before their descendants, breaking the object contract. We got affected by this issue while working on the copy tracing code. At about the same time, Axel Hecht <axel@mozilla.com> reported the issue and provided the test case used in this changeset. Thanks Axel. Running `hg perfancestors` does not show a significant difference between the old and the new version.

doc: use modern import style in runrst

hgweb: do not audit URL path as working-directory path Since hgweb is an interface to repository data, we don't need to prohibit any paths conflicting within the filesystem. Still an access to working files is audited by filectx.

hgweb: map Abort to 403 error to report inaccessible path for example Abort is so common in our codebase. We could instead introduce a dedicated type for path auditing errors, but we'll probably have to catch error.Abort anyway. As you can see, an abort message may include a full path to the repository, which might be considered information leak. If that matters, we should hide the message and send it to the server log instead.