Due to the way we check for missing commands, errexit will cause the script to quit too soon.

missing SUDO

use internal lzmaextract for xz and 7z as an alternative

Make sure binwalk always opens files with utf-8 encoding

In Python 3.4, if the interpreter is launched with e.g. LANG=C environment,
binwalk fails with UnicodeDecodeError, since it tries to decode included
magic files (such as src/binwalk/magic/linux) with ascii codec. This patch
makes sure that utf-8 codec is always used.