*Remote* branch name must be listed along with 'PUSH' keyword.

This requires predictable name of the remote, but as this whole slurping
thing is only meant for very dirty, very local scenarios, that should
not be problem.  (Other, more open scenarios are still possible, just
harder, as they probably should be.)

In that case (i.e. , the `${full#git_root}` would not work and print the full
basically full absolute path to git root.

 *  Add --force-* options to skipt .git-slurp-ok file checks.

 *  Allow passing path to slurp.

    You can slurp only a particular sub-tree.

 *  Improve commit message.

    Host has been dropped, and slurped paths are logged (as relative
    to worktree root).

 *  Die by dedicated function.

 *  Push only if allowed (a line containing single word PUSH found in
    .git-slurp-ok file)

 *  Allow working when deeper in git repo (but not if outside).

 *  Make permisson code readable (self-doc).

 *  Enclose in main() to allow for better hygiene.