Module needs to throw error if there is a structure mismatch.

Problem/Motivation

When importing single nodes, the module simply throws notification that node could not be imported. It does not mention
the reason for the failed import. This makes debugging difficult. I would suggest that the module throw a more meaningful error.

Steps to reproduce

1. Copy the export of a node.
2. Go to admin/content/import

Proposed resolution

After going through the code of the module, I could see that this is due to the fields not matching. The target content type should
have fields that match the node being imported.

Remaining tasks

We need to provide options to allow import for the matching fields in future.