Some shader fixes for OpenArena

Author: Gábor Udvari (gabor.udvari@gmail.com)
License: GPLv2 (see LICENSE.txt for more details)

Improved shaders (pack 2):
 - rocket splash, grenade splash, bfg splash improved
 - teleportThis: appearing in kaos2, flickering removed
 - various picmips: iconsprites.shader, newmenu.shader, hotmenu.shader

Improved shaders (pack 1):
 - textures/ctf/blue_telep2 and red_telep2: when observed from distance the image rounding results in a radial noise. To be able to change that, the shaders had to be edited to point to a file which is used in Q3 too, and those files are adjused. The two shaders are both defined in clown.shader and evil8.shader, remove the definition from there (I've only commented them out) and place them into oa_ctf.shader, since these definitions are OA specific.
 - rocket splash damage: when observed from distance, the image rounding results in a solid flashing rectangle. The shader file had to be adjusted.
 - BFG splash damage: same as rocket damage.
 - machinegun muzzle: when firing the machinegun a semi-transparent rectangle can be seen. The models/weapons2/machinegun/f_machinegun and models/weapons2/machinegun/flare images didn't have all black edges, and models/weapons2/machinegun/f_machinegun3 shader had a rgbGen identity declaration, which resulted in additional light coming from the weapon.