A psychologist who teaches at Johns Hopkins University came to Little Rock last week to work on his book that will propose that Bill Clinton has a mental condition that's actually an element of historic greatness.The author, John Gartner, contended in a previous book that Americans have achieved inordinate wealth because ours is a nation of people who had the gumption to take chances. From that heritage, his theory goes, we have seen the spread of a gene that causes the occasional person to have chemical and brain wave actions called hypomanic.