Private sector industry in the eurozone returned to growth in July, according to a closely-watched survey, boosting hopes that the single currency area will soon emerge from recession.   The Markit eurozone Purchasing Managers' Index (PMI), which measures business output, was 50.4 in July. A figure above 50 indicates expansion.   July's figure was up from 48.7 in June, and marks an 18-month high.   The eurozone has been in recession since the end of 2011.   "T...