By John S. McClenahen Executives this month appear to be more confident of their own job prospects. Nearly 48% of the 204 executives surveyed by ExecuNet, an Internet-based service, said that conditions in the executive employment market had improved during the past 30 days, a figure that was up five percentage points from March. (Some 52% described the market as flat and 1% said it was getting worse.) Some 41% of the executives were "confident" or "very confident" that the executive job market would improve during the next six months, a figure that was up four percentage points from March. Only 7% were "not confident" of improvement, and 52% were "somewhat confident." The survey results were released on April 16.