By John S. McClenahen Job prospects for executives are improving, suggests an ExecuNet survey. Some 39% of 112 executives surveyed are now "confident" or "very confident" that the executive employment market will improve during the next six months. That's up eight percentage points from the 31% who said so in November. In contrast, 13% are "not confident" the executive job market will be better in the next half year-the same level as in November--and 48%, compared with 56% in November, are "somewhat confident" that will happen. Executives now unemployed expect their job search will take 12.2 months; that slightly below November's expectation of 12.5 months.