fix genfilelist

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

1993/.filelist

@@ -1,10 +1,10 @@
 1993/1993.tar.bz2
-1993/Makefile
-1993/README.md
 1993/.filelist
 1993/.gitignore
 1993/guidelines.txt
 1993/index.html
+1993/Makefile
 1993/mkentry.c
+1993/README.md
 1993/rules.txt
 1993/.year