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