core: Add --tar-autocreate-parents option for commit

The tar files we're making of artifacts don't include parent
directories.  Now we could change the builder to make them, but we can
also just autocreate them on import.  Mode 0755 with no xattrs seems
OK here.

src/libostree/ostree-mutable-tree.c

@@ -221,6 +221,55 @@ ostree_mutable_tree_lookup (OstreeMutableTree   *self,
   return ret;
 }
 
+gboolean
+ostree_mutable_tree_ensure_parent_dirs (OstreeMutableTree  *self,
+                                        GPtrArray          *split_path,
+                                        const char         *metadata_checksum,
+                                        OstreeMutableTree **out_parent,
+                                        GError            **error)
+{
+  gboolean ret = FALSE;
+  int i;
+  OstreeMutableTree *ret_parent = NULL;
+  OstreeMutableTree *subdir = self;
+
+  g_assert (metadata_checksum != NULL);
+
+  if (!self->metadata_checksum)
+    ostree_mutable_tree_set_metadata_checksum (self, metadata_checksum);
+
+  for (i = 0; i+1 < split_path->len; i++)
+    {
+      OstreeMutableTree *next;
+      const char *name = split_path->pdata[i];
+
+      if (g_hash_table_lookup (subdir->files, name))
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "Can't replace file with directory: %s", name);
+          goto out;
+        }
+
+      next = g_hash_table_lookup (subdir->subdirs, name);
+      if (!next) 
+        {
+          next = ostree_mutable_tree_new ();
+          ostree_mutable_tree_set_metadata_checksum (next, metadata_checksum);
+          g_hash_table_insert (subdir->subdirs, g_strdup (name), next);
+        }
+      
+      subdir = next;
+    }
+
+  ret_parent = g_object_ref (subdir);
+
+  ret = TRUE;
+  ot_transfer_out_value (out_parent, &ret_parent);
+ out:
+  g_clear_object (&ret_parent);
+  return ret;
+}
+
 gboolean
 ostree_mutable_tree_walk (OstreeMutableTree     *self,
                           GPtrArray             *split_path,