Add missing (duh) file version header bytes
Avoid unconditional clobber of file header on each block put
Name each of the EQC tests
Remove out-of-order trailer

Add callback so backend_eqc test can deal with fold_keys() returning
more keys than actually written: e.g. put block # 3 will result in
fold_keys() believing that blocks #0, 1, and 2 will also exist.
If you try to fetch 0 or 1 or 2, you'll get not_found, which would
be correct of course.  But fold_keys() is optimized for speed and
not for 100% correctness -- fold_objects() and get() are correct.
Add get sibling resolution & app read repair