[metapost] Long numerical tokens with new number systems

[Toby Thurston]

The syntax for <numeric token> that MP inherits from Metafont allows for "one or more" decimal digits in the fractional part of a number.  So it's legal to write:

numeric pi;
pi = 3.141592653589793238462643383279502884197169399375105820974944592;
show pi;

This works ok with all the number systems except "decimal" which complains about excessive precision.
Here's what I get with each number system

>> "scaled"
>> 3.14159 )

>> "double"
>> 3.1415926535897931 )

>> "binary"
>> 3.1415926535897932384626433832795028 )

>> "decimal"
! Number is too precise (numberprecision = 34).
l.80 ...643383279502884197169399375105820974944592
                                                  ;
?
>> 3.141592653589793238462643383279503 )

Doesn't this behaviour seem to be a bit inconsistent?

Clearly, with decimal it would be possible to avoid the error message by writing this sort of thing:

   if numbersystem="decimal": numberprecision := 64; fi

before defining the constant, but it would be nice to have a consistent syntax across all number systems.

One other thing that I notice is that the final digit rounding looks wrong for double and binary.

Any comments?

Thanks, Toby