Servlet performance enhancements.

I made a few changes based off of hot method profiling using Java
Mission Control.

Enhancements include:

* replacing a contains? call with a hash lookup to prevent set
  generation
* removal of an unneeded ->LazyMap call
* using a macro to generate the ring request map, with the servlet
  fields stitched in to the initial base map creation instead of using a
  merge onto the LazyMap. They both use assoc underneath, but the former
  method does so on a transient, so is slightly faster.

Of these changes, the first yielded the biggest gains. For benchmarks,
see: https://gist.github.com/690633bd7270a8ae670a