time_format() claimed %H and %k would return at most two digits
(hours 0-23), but this coincided neither with actual behaviour
nor with docs.  this is not visible in simple queries; forcing
a temp-table is probably the easiest way to see this.  adjusted
the return-length appropriately; the alternative would be to
adjust the docs to say that behaviour for > 99 hours is undefined.
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Bug#19844: time_format in Union truncates values

time_format() claimed %H and %k would return at most two digits
(hours 0-23), but this coincided neither with actual behaviour
nor with docs.  this is not visible in simple queries; forcing
a temp-table is probably the easiest way to see this.  adjusted
the return-length appropriately; the alternative would be to
adjust the docs to say that behaviour for > 99 hours is undefined.