Christoph Büscher cd4634bdc6 Fix time zone rounding edge case for DST overlaps
When using TimeUnitRounding with a DAY_OF_MONTH unit, failing tests in #20833
uncovered an issue when the DST shift happenes just one hour after midnight
local time and sets back the clock to midnight, leading to an overlap.
Previously this would lead to two different rounding values, depending on
whether a date before or after the transition was rounded. This change detects
this special case and correct for it by using the previous rounding date for
both cases.

Closes #20833
2016-11-15 18:23:47 +01:00
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