exchange: abort on pushing bookmarks pointing to secret changesets (issue6159) Until now, if there is a bookmark points to a changeset which is in secret phase, hg will push the bookmark, but not the changeset referenced by that bookmark. This leaves the server bookmarks in a bad state, because that bookmark now points to a revision that does not exist on the server. This patch makes hg to abort on such cases. Differential Revision: https://phab.mercurial-scm.org/D6731