Avoid counting directory entries during a directory salvage.

Avoid counting directory entries during a directory salvage.

Add additional checks to HTREE directories.  We now check the count
and limit fields in the htree header, as well as assuring that the
hash table in each interior node is in ascending order.  We also
check to make sure all leaf nodes are have the expected depth in
the tree.

Updated test cases to deal with all of the above.