Refactor light tessellation
Use IterateLights() in more places
Fix potential NULL deref
Make sure the contents of tess are cleared before leaving RB_RenderInteractions*

Tess_StageIteratorLighting and similar use backEnd.currentLight to get the current light being rendered.
This is cleared to NULL later on, so make sure we finish before then.
fix invalid ptr deref
Clear the tess struct when finished in RB_RunVisTests
renderer: delete legacy renderer entity types (railgun, splash, ...)
renderers: we did not actually delete RT_BEAM

It is still used by cgame when the entity has eType ET_BEAM.
Althoguh no entity use it now we might want to keep it for later.
rendererGL: remove all stub D3D10 support
rendererGL: remove the inline D3D10 stub support
download-pk3.sh --verify
download-pk3.sh --source BASE_URL
Add a download-pk3.sh --source shorthand for Sourceforge mirrors
Use glsl builtin mix() instead of hand coded lerp
Remove unused varying in the generic shader
Add asserts to make sure the correct shader is bound when setting uniforms
Batch the geometry drawn by RB_Draw2dPolys
Fix GLSL compilation error: implicit cast of vec3 to vec4.

Using .xyzx is fine here since the last component is never used.
Also, storage is already allocated…
Merge branch 'master' into librocket