That flush feeling you had earlier this year was not just spring fever. In a trend many economists see continuing, personal income in the U.S. rose during the second quarter of this year. The Commerce Department says income jumped 1.9% from April through June, compared with a 1.3% hike in the first quarter of '94. More important, your buying power increased, as prices in the U.S. went up just seven-tenths of 1% in the spring. California tops a list of 11 states that posted higher-than-average income growth during the quarter, while South Dakota was the only state to show a drop in wages.