Use two parameter form of #system to avoid setting environment variables on the command line

* Partially reverts d02a01711c9b4e8fb5e402fc832d29bcc7a95e02
* Avoids setting environment variables as a command prefix which is not supported by the Windows command processor
Merge pull request #9 from cablegram/windows-fix-setting-env-vars

Use two parameter form of #system to avoid setting environment variables...