Per https://issues.apache.org/jira/browse/LUCENE-1349, we have made an
exception to Lucene's backward compatibility rules and marked
Fieldable as "changeable", namely meaning we will allow, on a case-by-
case basis, changes to the interface, meaning anyone who implements
there own Fieldable (which we suspect is very, very few people) may
have to make code changes when upgrading within a minor version. More
than likely, Fieldable will be deprecated and changed for 3.0 (when we
get there.)
This is noted prominently in CHANGES.txt and on the interface. Sorry
for the inconvenience.
Thanks,
Grant