I wanted an easy way to do nextfloat(a), taking into account that 'a' doesn't have the global BigFloat precision. I.e., what's the nextfloat of the 64-bit precision (in this case) BigFloat and return a 64-bit precision BigFloat.
I could write a function that does this, but I thought that there might be something easier than having to extract the precision of each BigFloat and nextfloat'ing with that global BigFloat precision.
