Error when Vundle is loading from multiple sources.

[annagrram]

It's quite common to see issues related to Vundle accidentally loading
from several sources.
Try to mitigate this issue by echoing an error.

[jdevera]

Thanks for the PR. However I think most problems with the duplicate install don't come because #rc or #begin is being called several times, but rather because people have one bundle/vundle, which they add to rtp manually, and then they do Plugin 'gmarik/Vundle.vim' which will install the second version that keeps updated.

Now, since everything in vundle is loaded on demand, they end up running bits from the updated vundle and bits from the one that is stagnant.

Which is why we also get the collections of "OMG Vundle tries to delete iself" issues :)

So, which error case is this one covering?

[annagrram]

Thanks for the comment.
You are right, I aimed for the first reason.
Fixed it to include the second, but both of them need to have this commit for it to work.