I don't think this is a compiler difference but rather a typo by Dave, although I can't figure out the original intent.  The wet bulb temperature is always lower than the "dry bulb" temperature.  Also the NOAA calculator, http://www.srh.noaa.gov/epz/?n=wxcalc_rh, gives a value of 294.33 for the pressure, temp and rh given.  This is much closer to the 294.287... value.  

Unfortunately the procedure to calculate wet bulb is iterative, so not an easy one to perform manually.