Rename garry.cpp to garry.alt.c and fix it

The reason I fixed it is indeed exactly as I said: I felt it has to work
because of the layout; it does indeed look like what the judges noted -
a rat dropping core.

Now one can use make alt and use garry.alt for the same results.

But why not garry.cpp? Because compilers will think it's C++ and besides
that these types of files are meant to be called .alt.c. The formatted
version provided by the author is still there of course.

1995/garry/.gitignore

@@ -1 +1,2 @@
 garry
+garry.alt