Oil slips after rally as market turns cautious

By Libby George LONDON (Reuters) - Oil prices fell on Tuesday after a two-day rally abated and trade remained volatile, due in part to a vote later this week in Britain that will determine whether the country leaves the European Union. A one-month ceasefire between the government and Nigerian militants whose attacks have curtailed the country's crude oil exports also added a bearish signal to a market that had firmed on the back of supply disruptions. Brent crude August futures were down $1.04 a