Convert NumberUtils.min/max array-accepting methods to use varargs

These will then be in competition with our three-arg variants, and we will have to validate that at least one arg is supplied. If for some reason v3.0 RC4 is unsuccessful we should tackle this right away so that we can remove the three-arg variants; else we will be living with them. Pretty sure compilers will just pick the three-arg variant when three args are specified.