/*
 * call-seq:
 *   easy.post_body = "some=form%20data&to=send"      => string or nil
 * 
 * Sets the POST body of this Curl::Easy instance.  This is expected to be
 * URL encoded; no additional processing or encoding is done on the string.
 * The content-type header will be set to application/x-www-form-urlencoded.
 * 
 * This is handy if you want to perform a POST against a Curl::Multi instance.
 */
static VALUE ruby_curl_easy_post_body_set(VALUE self, VALUE post_body) {