Add additional dir level to blobs/ about boar HOT 2 CLOSED

I agree that a repository can quickly become large enough to make it 
inconvenient to browse around the blobs manually. But then again, hundreds of 
thousands of files named something like "650ab14dd0caba8f71d2db9b4a3abb90" 
isn't very user friendly to begin with. I'm more concerned with the performance 
part. Do you have any numbers or examples backing up the performance problem 
claim? Boar performs these operations often:

* Checking the existence of a blob
* Opening a blob for reading
* Listing all the blobs

However, another problem is that fat32 only supports about 20000 file entries 
per directory (for 16 char long filenames), which allows a maximum of 5 million 
files in a repository for fat32. Not good. The easiest way out is of course to 
say that boar doesn't support fat32...

Closing this one for the time being, until someone can show in numbers that 
this is a real problem in some situations.