bundlerepo: replace basemap with the base field in the index Bundle revisions had some info in their fake revlog intries and some info in a dict with all the bundle revisions. This dict was used to get the stored data and to distinguish repo revisions from bundle revisions. Real repo revisions and bundle revisions will now be distinguished by comparing with the tip revision of the original repo. This reintroduces something similar to disktiprev which was unused and removed in a928865b4a4f and let that replace the O(reposize) dict.