We used to set PATH in emacs, but because babel executes "sh" via
shell-command, the configuration of the main shell may supersedes ours.

* doc/org/ltl2tgba.org, doc/org/ltl2tgta.org, doc/org/ltlcross.org,
doc/org/ltlfilt.org, doc/org/randltl.org, doc/org/tools.org,
doc/org/genltl.org: Move all local-file variable to...
* doc/org/.dir-locals.el: ... here.  And also set the PATH
in org-babel-sh-command.
* doc/org/init.el.in: Set the PATH in org-babel-sh-command.