branchcache: skip entries that are topological heads in the on disk file In the majority of cases, topological heads are also branch heads. We have efficient way to get the topological heads and efficient way to retrieve their branch information. So there is little value in putting them in the branch cache file explicitly. On the contrary, writing them explicitly tend to create very large cache file that are inefficient to read and update. So the branch cache v3 format is no longer including them. This changeset focus on the format aspect and have no focus on the performance aspect. We will cover that later.

Put here definitions of blacklists for run-tests.py

Create a file per blacklist. Each file should list the names of tests that you
want to be skipped.
File names are meant to be used as targets for run-tests.py --blacklist
option.
Lines starting with # are ignored. White spaces are stripped.

e.g. if you create a blacklist/example file containing:
 test-hgrc
 # some comment
 test-help
then calling "run-tests.py --blacklist blacklists/example" will exclude
test-hgrc and test-help from the list of tests to run.