methadone should support exec of arrays

[gchpaco]

Kernel.exec of a string, and anything that calls that (open4, open3, or indirectly the JVM runtime execs) performs an additional layer of tokenization; usually this is done by the shell on Unix systems. It is not difficult to create a difficult to escape string that, when passed to a shell, will cause some sort of security escalation; as a simple example imagine running

sh "rm #{file}"

where file could, say, be equal to "-rf /".

To avoid problems like these, this patch permits users to use exec with an array argument, which is supported by every execution strategy methadone supports. This will not invoke the shell, and so in this case

sh "rm", file

would probably return "file '-rf /' not found".

This change should be backwards compatible.

[davetron5000]

Thanks for doing this; this is a good call. I'll look into merging this tonight.

[davetron5000]

Once the tests pass on CI; I'll release a new gem. Thanks again!