Support path names starting with the '-' character

When the path begins with the '-' character, shell commands can
interpret the path name as an option.
To prevend that, '--' needs to be inserted before the path, which tells
the command that there are no more options.
Make the the script actually use /bin/bash

Under various distributions, /bin/sh can point to different shell than
/bin/bash (e.g. ash, dash).