store all heads of a branch in the branch cache All heads of branches will be stored in a new cache file 'branchheads.cache' within the .hg directory. The old 'branch.cache' file from older versions will be ignored. The new cache contents are formatted line-by-line as '{node} {branchtag}\n'. This is the same as the previous format. Now, every head is recorded in an oldest -> tipmost order. The localrepo.branchheads function is reworked to use the data from the cache.