fails:IO#sysseek on a file moves the read position relative to the current position with SEEK_CUR
fails:IO#sysseek on a file raises an error when called after buffered reads
fails:IO#sysseek on a file warns if called immediately after a buffered IO#write
fails:IO#sysseek on a file moves the read position relative to the start with SEEK_SET
fails:IO#sysseek on a file moves the read position relative to the end with SEEK_END
fails:IO#sysseek on a file can handle any numerical argument without breaking and can seek past EOF
fails:IO#sysseek on a file raises IOError on closed stream
