Introduce --benchmark-intense option
benchmark-intense: Generate individual work items from 2D work (tests host CPU rate of work production)
benchmark-intense: Simulate 250 KB generation transaction
benchmark-intense: Update work every second
benchmark-intense: Detect stale results
benchmark-intense: benchmark_update_interval constant in code
benchmark: Detect duplicate shares within 5 minutes
Bugfix: Fix CPU miner benchmarking within benchmark-intense mode
Merge branch 'benchmark_intense' into bfgminer