Prior to this commit, if a user passed in a script that was frozen,
the shell provisioner would fail to modify the script to replace line
endings for windows because the string was immutable. This commit fixes
that by dup'ing the string so that it can have its line endings replaced
Allows checksum validation on downloaded files via Util::Downloader
using MD5 and/or SHA1 checksums. This also integrates checksum validation
support with the shell provisioner for downloaded remote files.
