The `DirectoryEnd` member added by commit 52dbe654 (cmState: Record
the end position of each directory., 2015-08-01, v3.4.0-rc1~251^2~1)
actually tracks the current top-most scope in a directory's stack.  This
is evidenced by the use case in commit 3f4e5e8c (cmState: Return end
snapshot for GetBuildsystemDirectoryParent., 2015-09-01,
v3.4.0-rc1~100^2~1).  Rename the member to `CurrentScope` to clarify
this role.