dirstate: restore original estimation and update comment The former comment didn't reflect the content of the dirstate entries, the two nodes are a fixed header in the file and not per-entry. Split the documented entry into the path part and the fixed header. The heuristic itself is still valid, e.g. for the NetBSD src tree a maximum path size of 142 and an average of 49, resulting in 66 bytes per entry on average. Differential Revision: https://phab.mercurial-scm.org/D8850