Additional *sudo* changes.

Regarding #3: I had overlooked a couple of things, the first time around.

- Added DPT_ALLOW_FAKEROOT_OR_SUDO and DPT_CHOWN_FILES environment variables. The former is passed to `execute` as the argument for `fakeroot`.
- Updated README for new environment-variables.
- Changed DPT_FORCE_ENTROPY default to "false" instead of "no", to be consistent. The behavior should be the same.