Merge branch 'dt/cache-tree-repair'

Add a few more places in "commit" and "checkout" that make sure
that the cache-tree is fully populated in the index.

* dt/cache-tree-repair:
  cache-tree: do not try to use an invalidated subtree info to build a tree
  cache-tree: Write updated cache-tree after commit
  cache-tree: subdirectory tests
  test-dump-cache-tree: invalid trees are not errors
  cache-tree: create/update cache-tree on checkout

cache-tree.h

@@ -39,6 +39,7 @@ int update_main_cache_tree(int);
 #define WRITE_TREE_IGNORE_CACHE_TREE 2
 #define WRITE_TREE_DRY_RUN 4
 #define WRITE_TREE_SILENT 8
+#define WRITE_TREE_REPAIR 16
 
 /* error return codes */
 #define WRITE_TREE_UNREADABLE_INDEX (-1)