libcurl truncates usernames and passwords it reads from .netrc to
LOGINSIZE and PASSWORDSIZE (64) characters without any indication to
the user, to ensure the values returned from Curl_parsenetrc fit in a
caller-provided buffer.

Fix the interface by passing back dynamically allocated buffers
allocated to fit the user's input.  The parser still relies on a
256-character buffer to read each line, though.

So now you can include an ~246-character password in your .netrc,
instead of the previous limit of 63 characters.

Reported-by: Colby Ranger