Merge branch 'am/sparse-index-name-hash-fix'

Avoid adding directory path to a sparse-index tree entries to the name-hash, since they would bloat the hashtable without anybody querying for them. This was done already for a single threaded part of the code, but now the multi-threaded code also does the same. * am/sparse-index-name-hash-fix: name-hash: don't add sparse directories in threaded lazy init