dagop: use fctx.rev() consistently in filectxancestors() We can't use fctx.linkrev() to sort fctxs coming from multiple files. This was changed at 24b57c3899f8 due to performance issue, but we know we evaluate parent.rev() in revset anyway.

dagop: yield intro filectx by filectxancestors() This is the convention of dagop.*ancestors() functions.