Apricot feature, thats fit for trunk.

Baking would split non-planer quads in an unpredictable way, which is fine for rending but game engines often use a fixed order (0,1,2), (0,2,3) or (1,2,3) (1,3,0).
Added an option to use a fixed order when baking.

source/blender/makesdna/DNA_scene_types.h

@@ -274,7 +274,7 @@ typedef struct RenderData {
 	
 	/* Bake Render options */
 	short bake_osa, bake_filter, bake_mode, bake_flag;
-	short bake_normal_space, bpad;
+	short bake_normal_space, bake_quad_split;
 	float bake_maxdist, bake_biasdist, bake_pad;
 	
 	/* yafray: global panel params. TODO: move elsewhere */

source/blender/render/intern/include/render_types.h

@@ -499,6 +499,7 @@ typedef struct LampRen {
 #define R_NEED_TANGENT	32
 #define R_SKIP_MULTIRES	64
 #define R_BAKE_TRACE	128
+#define R_BAKING		256
 
 /* vlakren->flag (vlak = face in dutch) char!!! */
 #define R_SMOOTH		1

source/blender/render/intern/source/convertblender.c

@@ -3935,7 +3935,7 @@ static void set_fullsample_flag(Render *re, ObjectRen *obr)
 	}
 }
 
-static void check_non_flat_quads(ObjectRen *obr)
+static void check_non_flat_quads(ObjectRen *obr, int quad_flip)
 {
 	VlakRen *vlr, *vlr1;
 	VertRen *v1, *v2, *v3, *v4;
@@ -3997,11 +3997,13 @@ static void check_non_flat_quads(ObjectRen *obr)
 				xn= nor[0]*vlr->n[0] + nor[1]*vlr->n[1] + nor[2]*vlr->n[2];
 
 				if(ABS(xn) < 0.999995 ) {	// checked on noisy fractal grid
+					
 					float d1, d2;
 
 					vlr1= RE_vlakren_copy(obr, vlr);
 					vlr1->flag |= R_FACE_SPLIT;
 					
+					if (quad_flip==0) { /* nonzero quad_flip is used to force dividing one way */
 						/* split direction based on vnorms */
 						CalcNormFloat(vlr->v1->co, vlr->v2->co, vlr->v3->co, nor);
 						d1= nor[0]*vlr->v1->n[0] + nor[1]*vlr->v1->n[1] + nor[2]*vlr->v1->n[2];
@@ -4011,6 +4013,11 @@ static void check_non_flat_quads(ObjectRen *obr)
 					
 						if( fabs(d1) < fabs(d2) ) vlr->flag |= R_DIVIDE_24;
 						else vlr->flag &= ~R_DIVIDE_24;
+					} else if (quad_flip==1) {
+						vlr->flag &= ~R_DIVIDE_24;
+					} else { /* quad_flip == 3 */
+						vlr->flag |= R_DIVIDE_24;
+					}
 					
 					/* new vertex pointers */
 					if (vlr->flag & R_DIVIDE_24) {
@@ -4065,7 +4072,13 @@ static void finalize_render_object(Render *re, ObjectRen *obr, int timeoffset)
 			if((re->r.mode & R_RAYTRACE) && (re->r.mode & R_SHADOW)) 
 				set_phong_threshold(obr);
 			
-			check_non_flat_quads(obr);
+			if (re->flag & R_BAKING) {
+				/* Baking lets us define a quad split order */
+				check_non_flat_quads(obr, re->r.bake_quad_split);
+			} else {
+				check_non_flat_quads(obr, 0);
+			}
+			
 			set_fullsample_flag(re, obr);
 
 			/* compute bounding boxes for clipping */
@@ -5421,6 +5434,7 @@ void RE_Database_Baking(Render *re, Scene *scene, int type, Object *actob)
 	RE_init_threadcount(re);
 	
 	re->flag |= R_GLOB_NOPUNOFLIP;
+	re->flag |= R_BAKING;
 	re->excludeob= actob;
 	if(type == RE_BAKE_LIGHT)
 		re->flag |= R_SKIP_MULTIRES;

source/blender/src/buttons_scene.c

@@ -2150,6 +2150,10 @@ static void render_panel_bake(void)
 				 "Normalized displacement value to fit the 'Dist' range"
 		);
 	}
+	
+	uiDefButS(block, MENU, B_NOP, "Quad Split Order%t|Quad Split Auto%x0|Quad Split A (0,1,2) (0,2,3)%x1|Quad Split B (1,2,3) (1,3,0)%x2", 
+		10,30,190,20, &G.scene->r.bake_quad_split, 0, 0, 0, 0, "Method to divide quads (use A or B for external applications that use a fixed order)");
+	
 #if 0	
 	uiBlockBeginAlign(block);
 	uiDefButBitS(block, TOG, R_BAKE_OSA, B_DIFF, "OSA",		10,120,190,20, &G.scene->r.bake_flag, 0, 0, 0, 0, "Enables Oversampling (Anti-aliasing)");