A WORLD CRUISE topped the wish list of dream vacations if money was no object, according to a survey conducted for AIG Travel Guard, a travel insurance provider. Of those polled, 45% said an around-the-world cruise would be their No. 1 choice, followed by a month-long tour of Europe, an African safari, exploring Australia and a trip to a remote island without a phone or e-mail access. Despite their dreams, the survey also found that Americans have an average of 13 vacation days per year, as opposed to 28 days per year in the United Kingdom, 26 days in Canada and 45 days in Italy