* 1/2 JETHRO TULL. "The Crest of a Knave." Chrysalis. Tull-leader Ian Anderson used to be a champion of the free thinker, crusading against authority and conformity from the platform of his blues/Celtic/classical/rock music. Does that sound like the kind of guy who would put together a record through marketing research? That's what he did for the latest from Tull (now down to just Anderson, guitarist Martin Barre and bassist Dave Pegg), using listening parties in a dozen American radio markets to determine song selection and running order. Apparently, the 600 people who participated are real fond of Dire Straits, because that's what a lot of the record sounds like. There are some trademark Tull touches (Anderson's breathy flute, a few tricky time signature shifts), but they seem almost gratuitous. The lyrics, too carry little bark and even less bite. What has brought Anderson to this sorry state? Just listen to his voice: He sounds too tired to care.