SecureConnection.savefile() times out for large files

Created by: agraubert

Right now the timeout argument for SecureConnection.savefile() applies to the operation as a whole. This is inconsequential for small files, but can timeout on larger files where the transfer may not complete in time even though the two sockets are still actively communicating. The timeout parameter should apply to each chunk of the file, so the operation will continue as long as it receives at least one chunk per timeout interval.