Radiation Therapy, Combination Chemotherapy, and Amifostine in Treating Patients With Head and Neck Cancer

carcinoma of unknown primary, head and neck cancer, squamous cell carcinoma of unknown primary, stage iii squamous cell carcinoma of the lip and oral cavity, stage iv squamous cell carcinoma of the lip and oral cavity, stage iii squamous cell carcinoma of the oropharynx, stage iv squamous cell carcinoma of the oropharynx, stage iii squamous cell carcinoma of the nasopharynx, stage iv squamous cell carcinoma of the nasopharynx, stage iii squamous cell carcinoma of the hypopharynx, stage iv squamous cell carcinoma of the hypopharynx, stage iii squamous cell carcinoma of the larynx