nodemap: add a flag to dump the details of the docket We are about to add more information to the docket. We first introduce a way to debug its content. Differential Revision: https://phab.mercurial-scm.org/D7887

To run the tests, do:

cd tests/
python run-tests.py

See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.