bundle: support multiple destinations `hg outgoing` and `hg push` now support multiple destination. We do the same for `hg bundle`. Various other commands needs this kind of behavior and it would be create to factor this code out for their usage. However this is an adventure for another time. They are some minor change to the tests (in addition to the new test for the feature): * one because I updated a message to plurals, * another one because the error changed, and I actually find it clearer. Differential Revision: https://phab.mercurial-scm.org/D10414