Improve how to redefine macros in 2012/endoh1 alt

Now one can use variables SLEEP, TIMER, GRAVITY, PRESSURE and VISCOSITY,
rather than single letter variables. This is like other commits where
instead of having to redefine CDEFINE one can do something like

    make clobber SLEEP=50 GRAVITY=I TIMER=15 alt

Notice that some can be set to I rather than a number. See the author's
remarks for details.

The try.alt.sh script was updated for this improvement.

2012/endoh1/try.alt.sh

@@ -13,11 +13,11 @@ fi
 
 # unlike other try.sh/try.alt.sh scripts this one has two compiled binaries: one
 # which sets the gravity factor to I and the other that does not.
-make clobber CC="$CC" CDEFINE="-DA=10 -DG=I -DS=39000" alt >/dev/null || exit 1
+make clobber CC="$CC" TIMER=10 GRAVITY=I SLEEP=39000 alt >/dev/null || exit 1
 # we have to move the endoh1_color.alt to endoh1_color.alt3, not alt2, because
 # we have to use make clobber which would wipe out endoh1_color.alt2.
 mv endoh1_color.alt endoh1_color.alt3
-make clobber CC="$CC" CDEFINE="-DA=10 -DS=39000" alt >/dev/null || exit 1
+make clobber CC="$CC" TIMER=10 SLEEP=39000 alt >/dev/null || exit 1
 read -r -n 1 -p "Press any key run run slower fluid on endoh1_color.alt.c: "
 mv endoh1_color.alt3 endoh1_color.alt2
 # clear screen before continuing