fix: add suboption for configuring execution order of tools This could be accomplished by using wrapper scripts, but that would diminish the usefulness of the incremental formatting logic. Configuring execution order along with other things in the hgrc is probably more convenient anyway. This change highlights some awkwardness with suboptions and default values, which should be addressed separately. Differential Revision: https://phab.mercurial-scm.org/D5237

tests: fix up some import statements caught by Python 3 I'm curious how the import checker manages to be so much more pedantic in Python 3, but not enough to bother exploring. Differential Revision: https://phab.mercurial-scm.org/D5240