Apparently sending the tar output to stdout rather than a file causes tar to

Apparently sending the tar output to stdout rather than a file causes tar to
pad with trailing NULs, which slightly upsets old versions of gzip (1.2.4,
not 1.3.x), which upsets some of our correspondents.
Use -f to send it to a file instead. (It's not transparently clear what
happens when you mix -f and -C; I've tested this with ixion's tar, 1.13.25.)

Also add option -o to generate POSIX tar files, as for halibut/Makefile;
apparently this shuts up a `trailing garbage' error from WinZip.

[originally from svn r4429]