Publishing a local tar file on Windows (without Msys2) fails

[rveenker]

On Windows there exists a tar command (\Windows\System32) that can also be used for Alire. This eliminates the need for Msys2. However the commands and parameters are slightly different. The Alire command used is 'alr publish --tar --force'

To solve this issue I have created a fix and submitted a pull request. The pull request contains comments on the changes I made.

Note that this change is not covered by the test suite yet.

[mosteo]

Partially addressed by #631. I will try to come up with a safe subset of tar options for all versions that can appear.