/*
 * call-seq:
 *   field.content = "content"                        => "content"
 * 
 * Set the POST field content for this PostField. Ignored when a 
 * content_proc is supplied via either +Curl::PostField.file+ or 
 * +set_content_proc+.
 */
static VALUE ruby_curl_postfield_content_set(VALUE self, VALUE content) {