fix genfilelist

Fixed the sort for `make genfilelist` to ignore case
and to use the ${SORT} makefile variable.

1996/.filelist

@@ -1,10 +1,10 @@
 1996/1996.tar.bz2
-1996/Makefile
-1996/README.md
 1996/.filelist
 1996/.gitignore
 1996/guidelines.txt
 1996/index.html
+1996/Makefile
 1996/mkentry.c
+1996/README.md
 1996/rules.txt
 1996/.year