add logic to keep all level 0 and 1 files in page cache
reduce compaction threads to level that helped 2 drive stripe array
fadvise willneed now on 0, 1, and 2 ... i.e. compaction of unsorted files
make six overlap files the threshold instead of 4.  update all version_set.cc limits accordingly
raise imm and general thread counts based upon various test runs.
disable batch_count throttle.  brings back old AAE bug on slower drive arrays
Adjust throttle to be by key by database.  Fix write batch throttle logic to again exempt AAE
update vnode penalty logic to spread slowdown to all vnodes.  Also make level-1 penalty much lighter.
5 compact threads again, throttle NOT divided by open databases, level-1 now linear penalty
make throttle active whenever not default value of one
... getting closer ... landing level should never be considered as grooming.  faster it purges the less rewrite of same old data.  write amplification drops by one with these changes on large ingest test.
remove dead / unused code from throttle calculation
Merge pull request #117 from basho/mv-tuning4

mv-tuning4