added multithreaded upload of file sets
Merge pull request #1 from martinlippert/master

Mutlithreaded upload of filesets

Previously, all of the files in a fileset were uploaded sequentially.  This was problematic as it seems that each connection to S3 is throttled to a speed that is potentially lower than the available bandwidth of the sending host.  This change uploads the files in parallel (if a configuration option is set) to better utilize the full bandwidth of the sending host.