Resolution of SF bug #1002475 and patch #1003693; Header lines that end in

\r\n only get the \n stripped, not the \r (unless it's the last header which
does get the \r stripped).  Patch by Tony Meyer.

test_whitespace_continuation_last_header(),
test_strip_line_feed_and_carriage_return_in_headers(): New tests.

_parse_headers(): Be sure to strip \r\n from the right side of header lines.