CLN: clean up parser options

Also add a test to make sure that the C parser options validation is actually 
covered

example travis fail:

https://travis-ci.org/pydata/pandas/jobs/12171563

explanation (for the record):

if you print out `options` before this commit you'll see that they are all overwritten with a single value. Whatever this value is will depend on how the `_parser_defaults` dictionary happens to be ordered (which is random because of hashing). 

This caused a bug because the value of `value` is retained from the loop over `_parser_defaults`, and `default` is *not* reassigned in the two loops that follow the loop over `_parser_defaults`, so all the values end up being the same as the last argument that was iterated over from `_parser_defaults`.

magic explained :tada: