fix blocking of caching of seq load

we were setting nocache too late for the cache to see, move nocache
logic to _build()

ChangeLog

@@ -2,6 +2,7 @@
 - fix compiler warnings in ubuntu 13.10
 - reverse similarity rotation direction to match the convention used 
   elsewhere in vips
+- fix blocked caching of sequential load operations
 
 10/10/13	started 7.36.2
 - better jpeg startup

libvips/foreign/foreign.c

@@ -690,10 +690,6 @@ vips_foreign_load_temp( VipsForeignLoad *load )
 		printf( "vips_foreign_load_temp: partial sequential temp\n" );
 #endif /*DEBUG*/
 
-		/* You can't reuse sequential operations.
-		 */
-		load->nocache = TRUE;
-
 		return( vips_image_new() );
 	}
 
@@ -833,6 +829,13 @@ vips_foreign_load_build( VipsObject *object )
 
 	g_object_set( load, "flags", flags, NULL );
 
+	/* If the loader can do sequential mode and sequential has been
+	 * requested, we need to block caching.
+	 */
+	if( (load->flags & VIPS_FOREIGN_SEQUENTIAL) && 
+		load->access != VIPS_ACCESS_RANDOM ) 
+		load->nocache = TRUE;
+
 	if( VIPS_OBJECT_CLASS( vips_foreign_load_parent_class )->
 		build( object ) )
 		return( -1 );

libvips/iofuncs/cache.c

@@ -692,7 +692,7 @@ vips_cache_operation_buildp( VipsOperation **operation )
 
 	if( (hit = g_hash_table_lookup( vips_cache_table, *operation )) ) {
 		if( vips__cache_trace ) {
-			printf( "vips cache: hit\n" );
+			printf( "vips cache: found old operation\n" );
 			printf( "\t" );
 			vips_object_print_summary( VIPS_OBJECT( hit ) );
 		}
@@ -718,7 +718,7 @@ vips_cache_operation_buildp( VipsOperation **operation )
 				VIPS_OPERATION_NOCACHE )
 				printf( "vips cache: uncacheable\n" );
 			else
-				printf( "vips cache: miss\n" );
+				printf( "vips cache: caching new operation\n" );
 			printf( "\t" );
 			vips_object_print_summary( VIPS_OBJECT( *operation ) );
 		}