tree-wide: Use g_autoptr(Ostree*)

Part of cleaning up our usage of libglnx; we want to use what's in GLib where we
can.

Had to change a few .c files to `#include ostree.h` early on to pick up
autoptrs for the core types.

Closes: #1040
Approved by: jlebon

src/libostree/ostree-mutable-tree.c

@@ -22,9 +22,8 @@
 
 #include "config.h"
 
-#include "ostree-mutable-tree.h"
+#include "ostree.h"
 #include "otutil.h"
-#include "ostree-core.h"
 
 /**
  * SECTION:ostree-mutable-tree
@@ -183,7 +182,7 @@ ostree_mutable_tree_ensure_dir (OstreeMutableTree *self,
                                 GError           **error)
 {
   gboolean ret = FALSE;
-  glnx_unref_object OstreeMutableTree *ret_dir = NULL;
+  g_autoptr(OstreeMutableTree) ret_dir = NULL;
 
   g_return_val_if_fail (name != NULL, FALSE);
 
@@ -219,7 +218,7 @@ ostree_mutable_tree_lookup (OstreeMutableTree   *self,
                             GError             **error)
 {
   gboolean ret = FALSE;
-  glnx_unref_object OstreeMutableTree *ret_subdir = NULL;
+  g_autoptr(OstreeMutableTree) ret_subdir = NULL;
   g_autofree char *ret_file_checksum = NULL;
   
   ret_subdir = ot_gobject_refz (g_hash_table_lookup (self->subdirs, name));
@@ -261,7 +260,7 @@ ostree_mutable_tree_ensure_parent_dirs (OstreeMutableTree  *self,
   gboolean ret = FALSE;
   int i;
   OstreeMutableTree *subdir = self; /* nofree */
-  glnx_unref_object OstreeMutableTree *ret_parent = NULL;
+  g_autoptr(OstreeMutableTree) ret_parent = NULL;
 
   g_assert (metadata_checksum != NULL);