Scala-tools doesn't exist any more, which made lift-json-2.4 go away

Scala-tools is mirrored, but we can't find the old 2.9.2 version of
lift-json-2.4 anywhere.  2.5-M4 looks stable, is 2.10 compatible
and is available, so lets upgrade to that.

There appears to be no API level changes that should affect us