Decoration: Remove usage of multi-character constants
LuaVoxelManip: Allow liquid updates in non-mapgen VoxelManip objects
Mapgen V7: Fix out-of-bounds array access
BiomeDefManager: Fully initialize default biome
Add vector helpers
include mathconstants.h in numerics.cpp
Handle 0 vectors in vector.normalize()
When server sends late media, log to errorstream instead of crashing.

Do a check for valid num_files before doing
assert(!m_mesh_update_thread.IsRunning());

In particular, don't execute the assertion if all media has already
been received.
Directional fog + horizon colors, based on sun & moon positions at sunrise / sunset