Fixes bug from f64b1e1

I hastily made a change to natneg without testing it before assuming it
would work, and it didn't work. So this fixes it properly now.
Evaluate search queries as restricted Python

Something I threw together quickly this morning to make the search
server evaluations work properly. I'd like to build my own AST and
benchmark it with a large server list to see how much slower it is. In
any case, this implementation should usually be reliable despite any
slowness.