WOODBURY - Relatives of a Suffolk County Jail inmate who died in custody yesterday say they are planning to sue the county.Jail officials say Arthur Thomas was being held on bail before his trial for robbery charges. They say he suffered from an unspecified medical condition yesterday morning and was rushed to the hospital, where he died.Thomas' family says he had a tracheotomy last year, and that he had complained the jail wasn't allowing him to properly care for his throat.