Use 2× multisample antialiasing by default

[Calinou]

Follow-up to #487 (can be merged independently from it).

Given the low shader complexity and polygon counts, this should be safe to enable by default, even on integrated graphics.

This change applies to both the OpenGL 1 and OpenGL 2 renderers.

[ghost]

Enabling r_ext_multisample in GL2 destroys the sun rays (BUG!). Using only fbo multisampling is enough imo, using both just slows down the renderer.

[zturtleman]

r_ext_multisample 2 fails to create a window on Linux/X11 using some Intel integrated graphics (Debian 10, Intel(R) Core(TM)2 Duo CPU E8400). ioquake3's window creation should probably try disabling multisample if window creation fails. r_ext_framebuffer_multisample 2 does work however.

----- Client Initialization Complete -----
----- R_Init -----
SDL using driver "x11"
Initializing OpenGL display
Display aspect: 1.778
...setting mode -1: 1280 720
Couldn't get a visual
...WARNING: could not set the given mode (-1)
Initializing OpenGL display
Display aspect: 1.778
...setting mode -1: 1280 720
Couldn't get a visual
...WARNING: could not set the given mode (-1)
Setting r_mode -1 failed, falling back on r_mode 3
Initializing OpenGL display
Display aspect: 1.778
...setting mode 3: 640 480
Couldn't get a visual
...WARNING: could not set the given mode (3)
----- Client Shutdown (Client fatal crashed: GLimp_Init() - could not load OpenGL subsystem) -----
RE_Shutdown( 1 )
Hunk_Clear: reset the hunk ok
-----------------------
GLimp_Init() - could not load OpenGL subsystem

[Calinou]

Should we just default r_ext_framebuffer_multisample to 2 to solve this (and keep r_ext_multisample to its current value)? This would effectively enable MSAA only when using the OpenGL 2 renderer, but now that it's the default renderer, this should be fine.

Also, last time I tried, enabling framebuffer MSAA without enabling standard MSAA won't smooth out 3D models drawn on the HUD (such as the player's face). Admittedly, this is a minor issue.