branchcache: add attributes to track which nodes are verified Half of the cost of loading branchcache comes from verifiying all the nodes it has. We don't need to verify all the nodes in all the cases. Sometimes we need to verify only a set of nodes for a set of branches. We can ignore nodes of other branches as we are not going to read them. This patch introduces two attributes to branchcache class. _verifiedbranches is a set which will tell the branches for which it's head nodes are verified. _closedverified is a boolean which will tell whether all closednodes are verified or not. Another idea which I had was to keep a set of nodes which are verified, but it will be more ugly and difficult to track things on node level. Differential Revision: https://phab.mercurial-scm.org/D6156

branchcache: make entries a private attribute Differential Revision: https://phab.mercurial-scm.org/D6155

branchcache: introduce hasbranch() This will be used to check whether a branch exists or not. This will optimized in future. Differential Revision: https://phab.mercurial-scm.org/D6154

branchmap: drop branchcache.setdefault() (API) All the callers are updated to call setdefault of branchcache.entries Differential Revision: https://phab.mercurial-scm.org/D6153