repo: Add remote's keyring during GPG verification

This is pretty fugly but it at least avoids new public API.

src/libostree/ostree-repo-private.h

@@ -199,11 +199,21 @@ OstreeGpgVerifyResult *
 _ostree_repo_gpg_verify_with_metadata (OstreeRepo          *self,
                                        GBytes              *signed_data,
                                        GVariant            *metadata,
+                                       const char          *remote_name,
                                        GFile               *keyringdir,
                                        GFile               *extra_keyring,
                                        GCancellable        *cancellable,
                                        GError             **error);
 
+OstreeGpgVerifyResult *
+_ostree_repo_verify_commit_internal (OstreeRepo    *self,
+                                     const char    *commit_checksum,
+                                     const char    *remote_name,
+                                     GFile         *keyringdir,
+                                     GFile         *extra_keyring,
+                                     GCancellable  *cancellable,
+                                     GError       **error);
+
 gboolean
 _ostree_repo_commit_loose_final (OstreeRepo        *self,
                                  const char        *checksum,