Explicitly enable GL_ARB_draw_instanced to make sure gl_InstanceId is available
Keep l10n data in memory until the next vid_restart
Fix #extension pragma placement
Rename shader_t::anim_frames to shader_t::images
Replace 'const' with 'in'
Add const qualifier to conversion matrix declaration
Fix GLSL compilation warning
Fix viewport for shadowmaps and portals
Fix "preprocessor error: Macro names containing "__" are reserved." error
Fix "sampler arrays indexed with non-constant expressions is forbidden..."

..." in GLSL 1.30 and later"
Revert "Fix sampler arrays indexed with non-constant expressions is forbidden"
Minor code cleanup