make penalty for size overflow non-linear
address missing status update / status hiding relating to eleveldb issue #107
Merge branch 'mv-tuning7' of github.com:basho/leveldb into mv-tuning7
update comment about assumptions with penalty_double
add error logging to ReleaseRef.  await future work to establish recovery.
move auto file close from 4 to 10 days.  avoids nasty thrashing on weekly AAE tree building
Add retry to background write/close tasks.  Still gives up if retries also fail.
Close() performance counters upon Shutdown() call.
add shutdown logic for perf counters.  make sure retry logic only unmaps file once.
arg.  ReleaseRef() had two bugs that would hurt / fail retry.  Fixed.
when retry fails, force close so as not to leak handles and maybe give OS time to do the right thing eventually.
Raise key limit again now that dynamic block size is here to help.
move / remove Log() calls within mutex_ held regions
deal with compiler warning about an unused variable
merge cleanup
Merge branch 'mv-tuning7' into develop