r_texturemode

r_texturemode sets the texture detail (quality). In other words: r_texturemode controls the  texture interpolation by the graphics card.

Usage:
/seta r_texturemode GL_LINEAR_MIPMAP_NEAREST
then do:
/vid_restart

default: GL_LINEAR_MIPMAP_NEAREST

Note:

Very ugly:
GL_NEAREST_MIPMAP_NEAREST

Textures looks more smoother (bilinear):
GL_LINEAR_MIPMAP_NEAREST

Textures are interpolated in 3d also (trilinear):
GL_LINEAR_MIPMAP_LINEAR