The just-concluded holiday retail season continues to look strong, at least in top-line numbers provided by Spending Pulse. Sales increased more in 2010 than any time in the last four years, a sign that consumers may have found a comfort level despite the burdens of high unemployment. The data also shows that shoppers began returning to higher-end retailers rather than concentrate on discounters: Americans spent more on clothes, shoes, luxury goods and electronics in December than a year earlier, extending retail sales momentum that had been building since August, according to data released Wednesday.Figures released by MasterCard Advisors’ SpendingPulse, which...