Allow for third argument in file dict value to support explicit
file content type.
Fixing test to ensure it passes with python 3.
Make merge_kwargs case-insensitive when looking up keys.
test cleanup
Retrieve kwargs.keys() just once.
Merge pull request #1091 from vinodc/specify_file_content_type

Allow for explicit file content type support
Merge pull request #1092 from jianlius/case-insensitive-update

Make merge_kwargs case-insensitive when looking up keys.