WpImportedObject Needs to be more unique

[camfindlay]

From micmania1:
If you try to import multiple XML files you may get duplicate IDs which prevents new posts being imported.

Proposed fix:
Create a hash of the XML file, and append the post ID: d0be2dc421be4fcd0172e5afceea3970e2f3d940-ID

Another potential fix could be that we use the guid field of each post.

Yes I would tend to agree. Could be a good change for future version. Currently the module is a pretty quick a dirty way to migrate from one place to the other (SIlverStripe) and use case wasn't to import multiple blogs combining them into one.

Perhaps this is more a feature? Giving the ability to import multiple WP XML files into SS?