I'm getting (notice the negative sign): abs(big(-0.0)) = -0e+00 with 256 bits of precision
I think it would be better to have abs(big(-0.0)) return 0e+00 (for example, abs(-0.0) returns 0.0). Perhaps this could be fixed with an abs(::BigFloat) method. It seems that the problem is that abs(x::Real) is ifelse(x<0,-x,0), and -0 is not less than 0.
