SERVER-13084: hide cappedTruncateAfter inside Collection
SERVER-13084: move capped core methods into record store
SERVER-13084: remove all main capped methods into record store
SERVER-13084: move legalClientSystemNS into namespace_string
SERVER-13084: minor namespace_details.h cleaning
SERVER-13084: remove DiskLoc::drec
SERVER-13084: class IndexDetails -> struct
SERVER-13084: remove some magic DiskLoc calls