extended postfx and sniper hud fix

src/extras/shaders/contrast.frag

@@ -0,0 +1,18 @@
+uniform sampler2D tex0;
+uniform vec3 u_contrastAdd;
+uniform vec3 u_contrastMult;
+
+in vec4 v_color;
+in vec2 v_tex0;
+in float v_fog;
+
+out vec4 color;
+
+void
+main(void)
+{
+	vec4 dst = texture(tex0, vec2(v_tex0.x, 1.0-v_tex0.y));
+	color.rgb = dst.rgb*u_contrastMult + u_contrastAdd;
+	color.a = 1.0f;
+}
+