Fix overflow in strtod mantissa read when sizeof(int) is 2

[mlpce]

The mantissa read loop in strtod reads 18 digits using two ints to convert nine digits each. When sizeof(int) is 2 the conversion value overflows. To fix this the types of frac1 and frac2 have been changed to long.

Example:
printf("val f: %f\n", strtof("0.123456789012345678",NULL));
printf("val d: %f\n", strtod("0.123456789012345678",NULL));

Without fix:
val f: 0.000249
val d: 0.000249

With fix:
val f: 0.123457
val d: 0.123457