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.

2004/Makefile

@@ -62,7 +62,7 @@ all:
 	done
 	@echo '=-=-= ${YEAR} 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
 
@@ -110,7 +110,7 @@ everything:
 
 # diff orig source and source
 #
-orig_prog_diff:
+diff_orig_prog:
 	@echo '=-=-= ${YEAR} begin make $@ =-=-='
 	@echo
 	@for i in ${WINNERS} ; do \
@@ -124,7 +124,7 @@ orig_prog_diff:
 
 # diff alt source and source
 #
-alt_prog_diff:
+diff_alt_prog:
 	@echo '=-=-= ${YEAR} begin make $@ =-=-='
 	@echo
 	@for i in ${WINNERS} ; do \