obsolete: do not accept duplicated marker during exchange Before this patch, duplicated obsolescence markers could slip into an obstore if the bookmark was unknown locally and duplicated in the incoming obsolescence stream. Existing duplicate markers will not be automatically removed but they'll stop propagating. Having a few duplicated markers is harmless and people have been warned evolution is <blink>experimental</blink> anyway.

Merge with stable.

obsolete: stop doing membership test on list According to the Surgeon General, computer should not use list for membership testing because of the risk of being slow.

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