Correctly count unchanged entries when averaging
New field: Benchmark.on_summary

which defaults to yes, but can be set to false to prevent volatile or
uninteresting benchmarks from appearing in the summary. This fixes #176.
New manage.py command: recalculate_reports
Parameter --count to ./manage.py  recalculate_reports
Remove @require_GET from getcommitlog

As it is not a view. Fixes #175.