mesa: use enums for TEXTURE_x_INDEX values

Plus, put them in the order of highest to lowest priority to simplify
the texture_override() loop.
diff --git a/src/mesa/main/context.c b/src/mesa/main/context.c
index 0484879..75b3992 100644
--- a/src/mesa/main/context.c
+++ b/src/mesa/main/context.c
@@ -467,14 +467,15 @@
 
    /* Create default texture objects */
    for (i = 0; i < NUM_TEXTURE_TARGETS; i++) {
+      /* NOTE: the order of these enums matches the TEXTURE_x_INDEX values */
       static const GLenum targets[NUM_TEXTURE_TARGETS] = {
-         GL_TEXTURE_1D,
-         GL_TEXTURE_2D,
-         GL_TEXTURE_3D,
-         GL_TEXTURE_CUBE_MAP,
-         GL_TEXTURE_RECTANGLE_NV,
+         GL_TEXTURE_2D_ARRAY_EXT,
          GL_TEXTURE_1D_ARRAY_EXT,
-         GL_TEXTURE_2D_ARRAY_EXT
+         GL_TEXTURE_CUBE_MAP,
+         GL_TEXTURE_3D,
+         GL_TEXTURE_RECTANGLE_NV,
+         GL_TEXTURE_2D,
+         GL_TEXTURE_1D
       };
       ss->DefaultTex[i] = ctx->Driver.NewTextureObject(ctx, 0, targets[i]);
       if (!ss->DefaultTex[i])