When spring is in the air and the weather starts to heat up, so does your outdoor entertaining. But after a long winter, your outdoor furniture might be looking shabby, particularly under the bright, unforgiving glare of the sun. Before you hop on the Internet to order new furniture, see if there’s something you can do to revive that patio set, picnic table, garden glider, or favorite pair of lawn chairs. If your furniture is actually falling apart, it may be time to retire it. If it's…