Port now requires the JADETEX variable to be either "yes" or "no". If
"yes" then a dependency on print/jadetex is included (which in turn pulls
in all 30MB of TeTeX). If no then it is ignored. There is no default.

If ${JADETEX} is unset then pkg/JADETEX is shown to the user.

Set IS_INTERACTIVE to indicate this in the Makefile.