super block. We took it out in v1.8 library because it's meaningless
for the MULTI file. v1.8 library saves the EOA for the metadata file,
instead. But this caused some backward compatibility problem.
v1.8 library couldn't open the file created with v1.6 library. I
fixed the problem by checking the EOA value to detect the file
created with v1.6 library.
Tested on jam, koala, and heiwa.