core: [INCOMPATIBLE CHANGE] Re-split archive content into .file and .filecontent

This will allow us to use hard links again for user-mode checkouts,
rather than the hackish link cache.  It was pretty silly anyways to
have file objects be stored with just a small metadata header
prepended, but uncompressed.

Either they should be hardlinkable, or compressed (in pack files).

src/libostree/ostree-core.c

@@ -922,6 +922,23 @@ ostree_get_relative_object_path (const char *checksum,
   return g_string_free (path, FALSE);
 }
 
+char *
+ostree_get_relative_archive_content_path (const char        *checksum)
+{
+  GString *path;
+
+  g_assert (strlen (checksum) == 64);
+
+  path = g_string_new ("objects/");
+
+  g_string_append_len (path, checksum, 2);
+  g_string_append_c (path, '/');
+  g_string_append (path, checksum + 2);
+  g_string_append (path, ".filecontent");
+
+  return g_string_free (path, FALSE);
+}
+
 static char *
 get_pack_name (gboolean        is_meta,
                gboolean        is_index,