Automatically clean up files in data/moveChunk directory

I see a large number of files in the data/moveChunk directory. Googling around, I find that this is a dropoff directory for chunks that are being moved to another shard, but there is no provision to clear the space after the chunks are moved.
Questions:
1) At what point can I safely delete the files? There are many files prefixed with 'post.cleanup', are these safe to delete when found?
2) What other file prefixes are used? Are any of those files safe to delete?
3) Are there plans for MongoDB to automatically maintain this directory?
Thanks,
jlr