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