maint: use xsetmode, not xfreopen

maint: use xsetmode, not xfreopen

This fixes a bug noted by Eric Blake.  Code was using xfreopen to
change files to binary mode, but this fails for stdout when in
append mode.  Such code should use xsetmode instead.  This affects
only the port on platforms like MS-Windows which distiguish text
from binary I/O.
* bootstrap.conf (gnulib_modules):
Remove xfreopen and add xsetmode.  Sort.
* src/base64.c (main):
* src/cat.c (main):
* src/cksum.c (cksum):
* src/head.c (head_file, main):
* src/md5sum.c (digest_file):
* src/od.c (open_next_file):
* src/split.c (main):
* src/sum.c (bsd_sum_file, sysv_sum_file):
* src/tac.c (tac_file, main):
* src/tail.c (tail_file):
* src/tee.c (tee_files):
* src/tr.c (main):
* src/wc.c (wc_file): Use xsetmode, not xfreopen.