Feature request: list blocks in background

```
listBlocks can be done in the background in a worker thread while at the same 
time the filesystem is used for reading and writing. It doesn't seem like it 
should be necessary to block the mount until the listBlocks is finished.

```

Original issue reported on code.google.com by `jikam...@gmail.com` on 20 Oct 2010 at 2:32
