I tested this change on a Wikipedia index, with query "1", on a field
that has norms.
On Linux, JDK 1.6.0_13, I can see no performance difference (both get
7.2 qps, best of 10 runs).
On Mac OS X 10.5.6, I see some difference (13.0 vs 12.3, best of 10
runs), but given quirkiness I've seen on OS X's results not matching
other platforms, I think we can disgregard this.
Also, given the performance gain one sees when norms are disabled, I
think this is net/net a good change.
We'll leave the default as false (for back compat), but this setting
is deprecated with a comment that in 3.0 it hardwires to true.