Date locator for DAILY interval now returns middle of month

The matplotlib.dates.AutoDateLocator has a default of interval_multiples=True that attempts to align ticks with the start of meaningful intervals like the start of the month, or start of the day, etc. That lead to approximately 140-day intervals being mapped to the first and 22nd of the month. This has now been changed so that it chooses the first and 15th of the month, which is probably what most people want.