bug#10554: 24.0.92; No units specified (dimensionless quantities in Emacs Calc)

[Jay Belanger]

> We can define a trivial unit
>
> (add-to-list 'math-additional-units '(one "1" "One"))
>
> So every plain, dimensionless number in Calc can be converted to
> ones. "7" becomes "7 one",

This will automatically be done when "exact output units" option is
chosen.

>   Calc should interpret dimensionless numbers such as "7" equivalent
>   to "7 one" without the need to explicitly make this trivial
>   conversion in either direction.
...
> - If Calc finds a dimensionless number "7" on the stack, for unit
>   conversions it gets interpreted as "7 one"

This would break current convert-units behavior, where a dimensionless
number can be interpreted by the user as any unit.  This is why when the
user asks to convert a plain number, Calc asks for the old units.  Calc
was written that way on purpose, and is a feature of Calc's units
handling.