branchmap: make write a method on the branchmap object

branchmap: simplify write signature All necessary data (cache value and key) are now stored in the branchcache object. Any extra parameter is superfluous.

branchmap: add the tiprev (cache key) on the branchmap object The actual cache key used on disk is the (tipnode, tiprev) pair. There is no reason not to use the revision number for the in memory version.

branchmap: add the tipnode (cache key) on the branchcache object Gathering data and cache key paves the way to a lot of simplification.

branchmap: store branchcache in a dedicated object Value and key of branchcache would benefit from being hold by the same object. Moreover some logic (update, write, validation) could be move on such object. The creation of this object is the first step toward this move. The result will clarify branchcache related code and hide most of the detail in the class itself. This encapsulation will greatly helps implementation of branchcache for filtered view of the repo.

branchmap: `stream_in` write remote branchcache to local one The previous code was writing it to a non existent `branchcache` attribute. We now write is to the proper `_branchcache` attribute and initialize the `_branchcachetip` at the same time. We keep writing it to disk, the previous code had this part right.

bookmarks: fix head selection for merge with two bookmarked heads A type mismatch caused the search for the other head to fail. The code is fragile, and instead it ended up using the 'first' bookmark head, but the ordering is undefined and it could thus randomly use the wrong bookmarkhead and fail with: $ hg up -q -C e@diverged $ hg merge abort: merging with a working directory ancestor has no effect

branchmap: extract updatebranchcache from repo

branchmap: extract _updatebranchcache from repo

branchmap: _updatebranchmap does not need to be filtered The `_updatebranchmap` method on repo does not need to be filtered as all callers are already handling filtering themself. The fact it is filtered may had even lead to buggy behaviors, but by chances the method make very sparse use of the repo object.