BigDecimal#div should raise FloatDomainError if NaN is involved in 1.9
BigDecimal#div should return 0 if divided by Infinity and no precision given in 1.9
BigDecimal#div should raise ZeroDivisionError if divided by zero and no precision given in 1.9
BigDecimal#div should raise FloatDomainError if (+|-) Infinity divided by 1 and no precision given
Merge pull request #669 from atambo/bigdecimal_div_nan

Fix BigDecimal#div rubyspecs