Jean Shepherd, one-man talkathon, who has entranced and drawn his fanatical Followers into a night-people listeners' loyal bund over his WOR-Mutual Network, five-hour nightly radio program, has become a social issue and a cause celebre in New York and the surrounding half-dozen states where the program is heard. Within the past 10 day Shepherd has been in every New York newspaper and many national magazines, while he was whisked in and out of jobs, fired, re-hired: then cut off the air unceremoniously for mentioning an unadvertised product, a minor misdemeanor, which happen every day of the week. . .