lvm2-2.02.43 merged device-mapper into it (as version 1.02.29), sometimes since then or afterwards there has been a WHATS_NEW_DM file alongside WHATS_NEW that details the more important changes in the device-mapper code. This should be dodoc'ed too then. OTOH, there's a VERSION dodoc which is mostly useless - just the version number and the release date. But if VERSION is kept, then VERSION_DM should be also added similarly
Fixed in .88