Improve alt build of 1989/ovdluhe

One can now do

    make clobber P=5 alt

instead of the more awkward

    make clobber CDEFINE="-DP=5" alt

The try.alt.sh script was added and allows one to do

    P=5 ./try.alt.sh

If P is not specified it uses the default of the alt code (which checks
if it's defined first via #ifdef..#endif). Otherwise it uses the new
value. Of course if one specifies not an int or too high value (or maybe
too low - didn't try that) the program will fail. That is the fault of
the user. The author does note a reasonable range to try.

thanks-for-help.md

@@ -819,9 +819,11 @@ the program on each file four times in a row but rather does it on each file
 and starts over, doing it four times, to help with hopefully allowing different
 output.
 
-Cody also provided an [alternate version](/1989/ovdluhe/ovdluhe.alt.c) based on the
-author's remarks. See the README.md for details. The fix described above was
-fixed in this version too, after it was discovered and fixed.
+Cody also provided an [alternate version](/1989/ovdluhe/ovdluhe.alt.c) based on
+the author's remarks and the [try.alt.sh](/1989/ovdluhe/try.alt.sh) script that
+uses the alt code, allowing one to configure the alt build. See the README.md
+for details. The fix described above was fixed in this version too, after it was
+discovered and fixed.
 
 
 ## <a name="1989_paul"></a>[1989/paul](/1989/paul/paul.c) ([README.md](/1989/paul/README.md]))