pull: add support for tombstone commits

Add a new object type: OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT that is
used when a commit was intentionally removed.

If the remote repository doesn't use tombstone commits, do not fail on
a missing commit (change 0b795785dd).

When the remote repository uses tombstones, if a commit cannot be
found, check if the tombstone file is present and fail if it is not
present.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

src/libostree/ostree-core.h

@@ -56,15 +56,17 @@ G_BEGIN_DECLS
  * @OSTREE_OBJECT_TYPE_DIR_TREE: List of children (trees or files), and metadata
  * @OSTREE_OBJECT_TYPE_DIR_META: Directory metadata
  * @OSTREE_OBJECT_TYPE_COMMIT: Toplevel object, refers to tree and dirmeta for root
+ * @OSTREE_OBJECT_TYPE_COMMIT_TOMBSTONE: Toplevel object, refers to a deleted commit
  *
  * Enumeration for core object types; %OSTREE_OBJECT_TYPE_FILE is for
  * content, the other types are metadata.
  */
 typedef enum {
-  OSTREE_OBJECT_TYPE_FILE = 1,      /* .file */
-  OSTREE_OBJECT_TYPE_DIR_TREE = 2,  /* .dirtree */
-  OSTREE_OBJECT_TYPE_DIR_META = 3,  /* .dirmeta */
-  OSTREE_OBJECT_TYPE_COMMIT = 4     /* .commit */
+  OSTREE_OBJECT_TYPE_FILE = 1,                /* .file */
+  OSTREE_OBJECT_TYPE_DIR_TREE = 2,            /* .dirtree */
+  OSTREE_OBJECT_TYPE_DIR_META = 3,            /* .dirmeta */
+  OSTREE_OBJECT_TYPE_COMMIT = 4,              /* .commit */
+  OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT = 5,    /* .commit-tombstone */
 } OstreeObjectType;
 
 /**
@@ -73,14 +75,14 @@ typedef enum {
  *
  * Returns: %TRUE if object type is metadata
  */
-#define OSTREE_OBJECT_TYPE_IS_META(t) (t >= 2 && t <= 4)
+#define OSTREE_OBJECT_TYPE_IS_META(t) (t >= 2 && t <= 5)
 
 /**
  * OSTREE_OBJECT_TYPE_LAST:
  *
  * Last valid object type; use this to validate ranges.
  */
-#define OSTREE_OBJECT_TYPE_LAST OSTREE_OBJECT_TYPE_COMMIT
+#define OSTREE_OBJECT_TYPE_LAST OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT
 
 /**
  * OSTREE_DIRMETA_GVARIANT_FORMAT: