env: add -S option (split string for shebang lines in scripts)

[Assaf Gordon]

Hello,

Following recent discussion about shebang lines [1][2],
attached is a patch to add "env -S", with the same syntax as freebsd's 
env(1).

[1] https://lists.gnu.org/r/coreutils/2017-05/msg00020.html
[2] https://lists.gnu.org/r/bug-coreutils/2018-04/msg00031.html

Also included a small patch adding "--debug/-v" option.

It includes tests with close to %100 coverage, but no documentation yet.
If you think this is a good addition, I'll update the patch with 
documentation.

Comments welcomed,
 - assaf

env-v-S.patch.gz
Description: application/gzip