Replaced some opengl fixed functions with shaders. Temporary ShyotlUseLegacyRenderPath setting to debug if this change actually improves framerate at all (setting not tied to callbacks. Have to toggle shaders to have stuff pick up the setting change)

indra/newview/app_settings/shaders/class1/interface/twotextureaddF.glsl

@@ -0,0 +1,14 @@
+/** 
+ * @file twotextureaddF.glsl
+ *
+ * $LicenseInfo:firstyear=2007&license=viewerlgpl$
+ * $/LicenseInfo$
+ */
+ 
+uniform sampler2D tex0;
+uniform sampler2D tex1;
+
+void main() 
+{
+	gl_FragColor = texture2D(tex0, gl_TexCoord[0].xy)+texture2D(tex1, gl_TexCoord[1].xy);
+}