This method should throw IllegalArgumentException but:
- throws ArithmeticException for radix=0
- hangs for radix=1 or radix<0
- returns empty string for radix>Character.MAX_RADIX
 
==== For example: the following program hangs ====
import java.lang.Bignum;
class java_lang_Bignum_toString {
  public static void main(String args[]) {
     Bignum b=new Bignum(1);
     System.out.println(b.toString(1));
  }
}