GLES2: Fixes, clarifications to shaders

Resources/Textures/Shaders/stencil_mask.swsl

@@ -1,4 +1,5 @@
 void fragment() {
+    // Bypasses zTexture because only alpha is queried.
     if (texture2D(TEXTURE, UV).a == 0.0) {
         discard; // Discard if no alpha so that there's a hole in the stencil buffer.
     }