Upgrade ignores non-default "data" folder

[solival]

If I change local.php option $conf['savedir'] = '/some/other/path' all data will be stored in '/some/other/path'.
However, plugin will try to put new data folder to its default /[wikiroot]/data. So I have to copy all updated files from /[wikiroot]/data to /some/other/path manually. Would be great if upgrade plugin could handle this case automatically.

[splitbrain]

A pull request that matches extracted data directories with the appropriate config settings would be welcome.