don't cache vips_copy() or im_copy()

ChangeLog

@@ -1,5 +1,7 @@
 12/3/13 started 7.33.0
 - vipsthumbnail lets you specify the sharpening mask
+- turn off caching for im_copy()/vips_copy(), we use copy to stop sharing, and
+it's cheap so caching doesn't help anyway
 
 16/4/13 started 7.32.3
 - rename GETTEXT_PACKAGE as vips7.32 to help Debian (thanks Jay)

libvips/conversion/conver_dispatch.c

@@ -751,8 +751,10 @@ static im_function copy_desc = {
 
 	/* Can't set PTOP ... we don't want to zap the LUT, we want the real
 	 * image.
+	 *
+	 * Don't cache, since we use copy to stop sharing.
 	 */
-	IM_FN_PIO,			/* Flags */
+	IM_FN_PIO | IM_FN_NOCACHE,
 
 	copy_vec, 			/* Dispatch function */
 	IM_NUMBER( one_in_one_out ), 	/* Size of arg list */

libvips/conversion/copy.c

@@ -316,7 +316,12 @@ vips_copy_class_init( VipsCopyClass *class )
 	vobject_class->description = _( "copy an image" );
 	vobject_class->build = vips_copy_build;
 
-	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
+	/* We use copy to make fresh vipsimages to stop sharing, so don't
+	 * cache it. Plus copy is cheap.
+	 */
+	operation_class->flags = 
+		VIPS_OPERATION_SEQUENTIAL | 
+		VIPS_OPERATION_NOCACHE;
 
 	VIPS_ARG_IMAGE( class, "in", 1, 
 		_( "Input" ),