put needs to cope with files larger than 150GB

[keiranmraine]

If a file to be pushed back to a server exceeds 150GB the put fails.

The multipart chunk size needs to be automatically resized to allow the upload to proceed. The maximum number of parts is 10,000 and the default to 15MB:

--multipart-chunk-size-mb=SIZE
Size of each chunk of a multipart upload. Files bigger than SIZE are automatically uploaded as multithreaded-multipart, smaller files are uploaded using the traditional method. SIZE is in Mega-Bytes, default chunk size is 15MB, minimum allowed chunk size is 5MB, maximum is 5GB.