This code was indirectly included in at least 25 files: the 25 files
for which a dependency on string_utils.hpp has been added by a
consequence of its removal from animated.hpp. It should induce a small
compile time improvement.
* Minor speed optimizations (TODO: test whether these are actually
worth something)
* Fixed editor where nothing was displayed until terrains were rebuilt.
* Refactoring of all animation code in unit_display and halo.
* Adding animated.hpp, and the animated<T> template.
* Partial rewrite of image.?pp for speed: looking up images was what
was slowing the game
* Replacing all SDL_Surface*, and scoped_sdl_surface, with
shared_sdl_surface, which was renamed surface.
* Optimizing halo movement when unit moves
* Inlining some stuff for performance reasons
* Optimizing invalide_all redraws
* Adding support for animated terrain images
