bookmarks: rewrite pushing local bookmarks in "commands.push()" by "compare()" This patch adds "pushtoremote()", which uses "compare()" to compare bookmarks between the local and the remote repositories, to replace pushing local bookmarks in "commands.push()".

bookmarks: rewrite "updatefromremote()" by "compare()" To update entries in bmstore "localmarks", this patch uses "bin(changesetid)" instead of "repo[changesetid].node()" used in original "updatefromremote()" implementation, because the former is cheaper than the latter.

bookmarks: add function to centralize the logic to compare bookmarks This patch adds "compare()" function to centralize the logic to compare bookmarks between two repositories.