dc(1): fix input of non-decimal fractional numbers
Inputting fractional non-decimal numbers has never worked correctly in our
OpenBSD-derived dc(1). It truncates the number to a number of decimal places
equal to the number of hexadecimal (or whatever base) places given on the
input. That's unacceptable, because many numbers require more precision to represent in base 10 than in their original bases.
Fix this bug by using as many decimal places as needed to represent the input,
up to the maximum of the global scale factor.
This has one mildly surprising side effect: the scale of a number entered in
non-decimal mode will no longer equal the number of hexadecimal (or whatever
base) places given on the input. I think that's an acceptable behavior change,
given that inputting fractional non-decimal numbers never worked in the first
place, and the man page doesn't specify whether trailing zeros on the input
should affect a number's scale.