tersestatus: re-implement the functionality to terse the status The previous terse status implementation was hacking around os.listdir() and was flaky. There have been a lot of instances of mercurial buildbots failing and google's internal builds failing because of the hacky implementation of terse status. Even though I wrote the last implementation but it was hard for me to find the reason for the flake. The new implementation can be slower than the old one but is clean and easy to understand. In this we create a node object for each directory and create a tree like structure starting from the root of the working copy. While building the tree like structure we store some information on the nodes which will be helpful for deciding later whether we can terse the dir or not. Once the whole tree is build we traverse and built the list of files for each status with required tersing. There is no behaviour change as the old test, test-status-terse.t passes with the new implementation. Differential Revision: https://phab.mercurial-scm.org/D985