S3 Improvements, fixes for large numbers of tracked files and support for --short status output

S3 Improvements, fixes for large numbers of tracked files and support for --short status output (only printing the number of files that are expanded, not expanded, pushed etc.).
Also fixes errors when tracking files with spaces in the path ( sync.update_index ).
Implemented autodownload setting and skipping of stubs during clean which was mentioned as TODO in the scripts (and I happened to need that). Added some error handling for downloading files from S3 (e.g if the file does not exist on the server). Some formatting changes.