core: Only do devino scan on commit (speeds up pull)

When fetching data remotely, there's no point to the devino scan
because we're not going to be committing local files.

Only do it for "commit".

src/libostree/ostree-repo.c

@@ -1276,6 +1276,7 @@ devino_cache_lookup (OstreeRepo           *self,
 
 gboolean
 ostree_repo_prepare_transaction (OstreeRepo     *self,
+                                 gboolean        enable_commit_hardlink_scan,
                                  GCancellable   *cancellable,
                                  GError        **error)
 {
@@ -1285,13 +1286,14 @@ ostree_repo_prepare_transaction (OstreeRepo     *self,
 
   self->in_transaction = TRUE;
 
-  if (!self->loose_object_devino_hash)
+  if (enable_commit_hardlink_scan)
     {
-      self->loose_object_devino_hash = g_hash_table_new_full (devino_hash, devino_equal, g_free, g_free);
+      if (!self->loose_object_devino_hash)
+        self->loose_object_devino_hash = g_hash_table_new_full (devino_hash, devino_equal, g_free, g_free);
+      g_hash_table_remove_all (self->loose_object_devino_hash);
+      if (!scan_loose_devino (self, self->loose_object_devino_hash, cancellable, error))
+        goto out;
     }
-  g_hash_table_remove_all (self->loose_object_devino_hash);
-  if (!scan_loose_devino (self, self->loose_object_devino_hash, cancellable, error))
-    goto out;
 
   ret = TRUE;
  out:

src/libostree/ostree-repo.h

@@ -77,6 +77,7 @@ GFile *       ostree_repo_get_file_object_path (OstreeRepo   *self,
                                                 const char   *object);
 
 gboolean      ostree_repo_prepare_transaction (OstreeRepo     *self,
+                                               gboolean        enable_commit_hardlink_scan,
                                                GCancellable   *cancellable,
                                                GError        **error);