fix pattern matching

fix function_clause error:

        {error,
        {error,
            {'EXIT',
                {{function_clause,
                     [{ibrowse_http_client,do_send_body_1,
                          [{{ok,<<>>},

The case {Function, State} wasn't took in consideration while handling
the body.
Merge pull request #110 from refuge/fix/fun-with-state-pattern-matching

fix send_body pattern matching. Thanks Benoit