Close-to-zero TTL handling was bit iffy. Addressed.
Converted asserts to object-specific ones, and removed last debug.
Added TTL-correctness checks, and fixed cache_flush handling on stuff learned via OSPF.
Debug/assert changes to use self:, and fixed one nsec ttl corner case.
Fixed the query-while-interested code to work better.
Some refactoring of TTL code; still unable to reproduce one bug with tests, but hopefully this fixes it.