Merge pull request #110 from aptivate/allow_override_resource_field_construction

Allow ModelResources to modify field settings during/after construction.
Merge branch 'master' of https://github.com/bmihelac/django-import-export
Fix error message to name the correct starting model.

Conflicts:

	tests/core/tests/resources_tests.py
Merge branch 'fix_link_to_nonrelation_field_error_message_2'