summary: make "incoming" information sensitive to branch in URL (issue3830) Before this patch, "incoming" information of "hg summary --remote" is not sensitive to the branch specified in the URL of the destination repository, even though "hg pull"/"hg incoming" are so. Invocation of "discovery.findcommonincoming()" without "heads" argument treats revisions on branches other than the one specified in the URL as incoming ones unexpectedly. This patch looks head revisions, which are already detected by "hg.addbranchrevs()" from URL, up against "other" repository, and invokes "discovery.findcommonincoming()" with list of them as "heads" to limit calculation of incoming revisions.