Add PREFER_SHA256_FILE_HASH flag. WHEN SHA256_FILE_HASH flag is set, the client supports both md5 and sha256. This allows a client to talk to both server configured to use md5 hash and server configured to use sha256 hash. The hash can be chosen by using the --hash commandline switch for iput. The prefer flag tells iput which hash to use when --hash is absent. This doesn't affect the behavior of the server, because the server has to either use md5 or sha256 but not both.

git-svn-id: svn://irodssvn.ucsd.edu/trunk@5641 ea137bd6-aa86-47b6-b90d-b101d9f19a90
Add one more file to r5641

git-svn-id: svn://irodssvn.ucsd.edu/trunk@5642 ea137bd6-aa86-47b6-b90d-b101d9f19a90