by Pauline DE DEUS MEXICO CITY, Mexico (AFP) — Colorful gondolas lazily ferry tourists around the floating gardens of Mexico City’s Xochimilco district, but not all is green in this idyllic vestige of the Aztec empire increasingly choked by urbanization. Criss-crossed with natural canals and artificial islands, Xochimilco is the last reminder of how the Aztecs lived 500 years ago at the time the Spanish conquistadors arrived, when Mexico City was mostly covered in water. […]