tests: add test for hg-test-mode emacs code This is just coverage for the compilation-mode support, but that was enough of a hassle that I wanted to have it covered somehow. Test methodology is _extremely_ cargo-culted from the test for compilation-mode in emacs, so I still have no idea what I'm doing. Differential Revision: https://phab.mercurial-scm.org/D6003

#require docutils gettext

  $ $TESTDIR/check-gendoc fr
  checking for parse errors