fails:IO#sysseek sets the offset
fails:IO#sysseek converts arguments to Integers
fails:IO#sysseek does not accept Bignums that don't fit in a C long
fails:IO#sysseek raises IOError on closed stream
fails:IO#sysseek moves the read position relative to the current position with SEEK_CUR
fails:IO#sysseek raises an error when called after buffered reads
fails:IO#sysseek moves the read position relative to the start with SEEK_SET
fails:IO#sysseek moves the read position relative to the end with SEEK_END
