[tz] Direct implementation of mktime_z

[Ted Phelps]

On 27/9/22 14:17, Bradley White wrote:

> Assuming we want to model the proleptic Gregorian calendar, it would 
> be nice if the output was linear over all inputs.  At the moment, for 
> example, daynum(0, 2, 29) and daynum(0, 3, 1) both return -305.

Ah, nice find!  I forgot to compensate for division by negative numbers, 
and my test suite doesn't cover times before about 1800. I'll fix both 
shortcomings shortly.

-Ted