This will improve performance on very large date ranges, basically avoid selecting 12 month archives.
Users regularly mention slow date ranges reports for multi year. This improvement should be really beneficial for these reports (ie. since Piwik tracks up to now will use less than 10 archives, instead of possibly 50 now!).
In 3e16dd5: refs #2270 use year range if possible
refs #2270 use year range if possible