A common Slideshow pattern is to put a subset of slides in its
own module with a `run-slides' function, and then you'd
(un)comment a `(run-slides)' call at the end of the module to
work on the subset by itself. Now, you can write
`(module+ main (run-slides))' atthe end of the module and not
have to comment it out. Adding `main' support to the `slideshow'
executable makes it more consistent with using `racket' directly.
Checking first for a `slideshow' submodule makes it possible
for `slideshow' and `racket' to do different things, in case
that's useful.
I originally picked "under" as the preposition to go before
a platform name, but obviously you should build "on" a
platform, and "under" suddenly annoys me. The choice of "on"
is now codified in the documentation style guide. Meanwhile,
"Unix" insted of "X" seems more clear and consistent in the
`racket/gui' docs.
More usefully, this patch also fixes a few out-of-date
platform-specific claims.
