ByJohn S. McClenahen The National Federation of Independent Business' (NFIB) Small Business Optimism Index reached 103 (1986=100) in June, continuing an unprecedented 15-month string of readings of 100 or more. " . . . Profit trends are favorable, and capital spending is solid," says NFIB. However, although small business owners, led by manufacturing, continued to create jobs in June, it wasn't at the same pace as earlier this year. And its June data contained a "surprise," says NFIB. Capital-spending plans "unexpectedly" dropped four percentage points.