fails with "Error in MD5 checksums" when dd isn't available

[moritzschepp]

I was running one of gog.com installers (they are all created with makeself it looks like) in an env where dd wasn't available. The installer then swallows the "dd: command not found" and finally reports "Error in MD5 checksums".

Not sure if this is a supported case.

Somewhat related: #161

[megastep]

Well it is true that we had to deal with different variants of dd being available, but I've never heard of an environment where the command is just not available. It's a very basic command that we rely on pretty extensively to parse the archives. We could add a check and fail with an error if it is not available though.