Rename diff Makefile commands

Renamed these Makefile rules:

    orig_prog_diff ==> diff_orig_prog
    alt_prog_diff ==> diff_alt_prog

Updated thanks-for-fixes.md and faq.md accordingly.

Makefile

@@ -51,7 +51,7 @@ all:
         done
 	@echo '=-=-=-=-= IOCCC complete make $@ =-=-=-=-='
 
-.PHONY: all alt data everything orig_prog_diff alt_prog_diff \
+.PHONY: all alt data everything diff_orig_prog diff_alt_prog \
 	clean clobber install love haste waste maker easter_egg \
 	sandwich supernova deep_magic magic charon pluto
 
@@ -93,7 +93,7 @@ everything:
 
 # diff orig source and source
 #
-orig_prog_diff:
+diff_orig_prog:
 	@echo '=-=-=-=-= IOCCC begin make $@ =-=-=-=-='
 	@-for i in [12][0-9][0-9][0-9]; do \
             if [ -f $$i/Makefile ]; then \
@@ -105,7 +105,7 @@ orig_prog_diff:
 
 # diff alt source and source
 #
-alt_prog_diff:
+diff_alt_prog:
 	@echo '=-=-=-=-= IOCCC begin make $@ =-=-=-=-='
 	@-for i in [12][0-9][0-9][0-9]; do \
             if [ -f $$i/Makefile ]; then \