catch errors from system commands

[matyaskopp]

There are a lot of system calls inside the Perl code, and the output code is not caught, so only the error message (usually without the error keyword) is printed to the log. see #883 (comment)
eg

sh: 1: rename: Argument list too long

Catch these errors and add the keyword ERROR, so it will appear in the ParlaMint-XX.error.log output

[TomazErjavec]

This won't be fixed for 5.0, so moving it to Future milestone.