dirstate-v2: adjust the meaning of directory flags...
dirstate-v2: adjust the meaning of directory flags
Tracking directory "explicitly" give use the opportunity to distinct between
entry that are untracked because they are part of the directory structure and
entry that are ignored/unknown files on the files system.
The help is adjusted to the new semantic and the code now comply to it for both
read and write.
Differential Revision:
https://phab.mercurial-scm.org/D11694
