Madison police say they have arrested a 25-year-old homeless man for threatening to cut the throats of two people early Monday morning.  The 39-year-old man and 23-year-old woman had taken shelter in a downtown parking garage during heavy rain.  Tyler Hawks is accused of lunging at the couple and slashing at them with a broken bottle.   Hawks had been in a relationship with the woman in the past and he was angry to see her with another man.  All three people involved in Monday’s incident are homeless.  Hawks was found not far from the parking garage and was taken into custody without incident.