Try to generate the exe in a more portable manner.

/bin/sh on linux will pass the command and args as the command to
/usr/bin/env on the shebang line, so we use exec instead and exploit
the 'loophole' with zip files that allows garbage at the head of the
zip.
Merge pull request #51 from tobias/genexe-linux

Try to generate the exe in a more portable manner.