Movng to sci-mathematics

Package-Manager: portage-2.2.0_alpha176
move sci-libs/flint to sci-mathematics/flint

Package-Manager: portage-2.2.0_alpha176
Completing the move from sci-libs/flint to sci-mathematics/flint. This is done to match the main
tree as sage 5.10 will use flint 2.3 from the tree - hopefully.