The Singapore Environment Ministry is mulling proposals to give the owners of 1,400 coffee shops island-wide one-time financial incentives to upgrade their toilets.   Speaking at the opening of the inaugural World Toilet Summit 2001 at Singapore Expo yesterday [Monday], acting environment minister Lim Swee Say explained the rationale behind the proposals: "When people use upgraded toilets, they take better care, making sure they do not litter the place and aim properly.