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