Change fix for T44530 which caused a "regression".

Looks like the previous commit here is really correct and fixes cases of
distortion that were in mirror-subsurf combination since blender 2.5.

This may cause some changed files in which case we will be adding an
option, but it is expected this will only happen with low res models,
and hand painted textures, and the better distortion here compensates
for that enough to consider not adding a compatibility option yet.

Leaving the facemap winding argument as is just in case we do consider
to add the option.

source/blender/blenkernel/intern/subsurf_ccg.c

@@ -300,7 +300,11 @@ static int ss_sync_from_uv(CCGSubSurf *ss, CCGSubSurf *origss, DerivedMesh *dm,
 	float uv[3] = {0.0f, 0.0f, 0.0f}; /* only first 2 values are written into */
 
 	limit[0] = limit[1] = STD_UV_CONNECT_LIMIT;
-	vmap = BKE_mesh_uv_vert_map_create(mpoly, mloop, mloopuv, totface, totvert, 0, limit, false);
+	/* previous behaviour here is without accounting for winding, however this causes stretching in
+	 * UV map in really simple cases with mirror + subsurf, see second part of T44530. Also, initially
+	 * intention is to treat merged vertices from mirror modifier as seams, see code below with ME_VERT_MERGED
+	 * This fixes a very old regression (2.49 was correct here) */
+	vmap = BKE_mesh_uv_vert_map_create(mpoly, mloop, mloopuv, totface, totvert, 0, limit, true);
 	if (!vmap)
 		return 0;