Files in subdirectories of directories that have the nodump flag set

Files in subdirectories of directories that have the nodump flag set
are sometimes incorrectly being dumped.

The problem arises because the subdirectory only gets its entry
cleared from usedinomap if it is also present in dumpinomap, and it is
the absence of a directory in usedinomap that internally indicates
that the directory is under the effects of UF_NODUMP (either directly
or inherited).

PR:		32414
Submitted by:	David C Lawrence <tale@dd.org>