Upgrade checker needs to re-run previous command on success in order to guarantee updates

[deajan]

Since we now distribute non single binary files, our previous upgrade path doesn't work anymore.

We need to run upgrader before anything else in order to prevent later program issues interfering with updates. But, we also need a guarantee that the initial program call will be done. We must find (a good) way for this pseudo code:

copy current dist to old dist move new dist to current dist run with --version on succees run new version with sys.argv[1:] on failure delete current dist move old dist to current dist

[deajan]

Currently in testing stage but implemented in v3.0.0-rc5

[deajan]

Now tested in master for windows. Currently rebuilding binaries for more tests, especially with legacy arches.

[deajan]

Done in master.