This commit tweaks some unit names:
- Remove `name_alt` for square mile "sq m" and cubic mile "cu m" as
they could easily be confused with meters.
- Correct plural forms for the ton units: rename "ton" to "tonne" for
the metric ton, and "tonnes" to "tons" for the imperial (short) ton.
Identifiers are unchanged.
- Swap `name_short` and `name_alt` for metric ton, hour, and second,
as `name_short` is used for UI display and should use the official
symbol. Keep the other form as `name_alt` for input.
- Use "t" and "tn" respectively as short names for the metric and
imperial (short) ton.
- Rename radian's short name "r" to "rad", keep it as alt name.
- Introduce alt names for km/h (kph), arcminutes (amin),
arcseconds (asec), for convenience.
References:
- https://en.wikipedia.org/wiki/Ton
- https://en.wikipedia.org/wiki/Tonne
Ref: !116762
299e112d1a