If a field name contains non-ascii characters in a 2.3.x index, then
on upgrade to 2.4.x unexpected problems are hit. It's possible to hit
a "read past EOF" IOException; it's also possible to not hit an
exception but get an incorrect field name.
This was caused by
LUCENE-510, because the FieldInfos (*.fnm) file is
not properly versioned.
Spinoff from http://www.nabble.com/Read-past-EOF-td23276171.html