yonik mentioned it would be a good idea back when I added reopen in, kind of as a failsafe. I pushed it into 243, but it doesnt really belong there.
Reopen has now been in use some, and I think a failsafe is less of a concern, but it could still come in handy - when we allow custom IndexReaders,
there may be a reason to not reopen it. Or if we find a new Lucene reopen bug or something when someone is doing something obscure,
1.4 users will be able to turn it off rather than jumping to trunk for a fix or waiting for 1.4.1 or whatever.