Remove use of ignore_missing_ack obsolete setting in Engine.start_cfg

Ignore-this: 97aff8f71316fa84b1a8546f639dccad

darcs-hash:20090819121208-1e3d8-0bc55c08dafcd0d84d3ff4a811eae2f89f3340ef
Modified lookup module to create a new Resolver for each lookup request

Ignore-this: 9c756c44faecb5aa8d93263a9f6357d5

darcs-hash:20090819131001-1e3d8-9c5989403aca63e6c8ec53bb5a69716056b75cc0