Fixes our post processing shaders so they work under OpenGL ES 3.0

Most of our shaders relied on implicit int->float conversions.
This fixes the assumption that this is allowed

Data/Sys/Shaders/acidtrip.glsl

@@ -7,5 +7,5 @@ uniform vec4 resolution;
 
 void main()
 {
-  ocol0 = (texture(samp9, uv0+resolution.zw) - texture(samp9, uv0-resolution.zw))*8;
+  ocol0 = (texture(samp9, uv0+resolution.zw) - texture(samp9, uv0-resolution.zw)) * 8.0;
 }