Make it so we don't have to 'git add -f' particular files like
po/POTFILES.in all the time (tested by fixing one of our
special-case files as part of the patch).

* .gnulib: Update to latest.
* bootstrap: Resync from coreutils.
* .gitignore: Sort whitelist entries correctly, including ignoring
files rather than directories.
* m4/virt-compile-warnings.m4: Convert tabs to space.