Avoid extra allocations in Asn1Time Display impl

use ffi;

use libc::c_long;

use std::{ptr, fmt};

use std::fmt;

use std::ptr;

use std::slice;

use ffi;

use std::str;

use {cvt, cvt_p};

use bio::MemBio;

impl fmt::Display for Ref<Asn1Time> {

    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        unsafe {

            let mem_bio = try!(MemBio::new());

        let as_str = unsafe {

            try!(cvt(ffi::ASN1_TIME_print(mem_bio.as_ptr(), self.as_ptr())));

            String::from_utf8_unchecked(mem_bio.get_buf().to_owned())

        };

        write!(f, "{}", as_str)

            write!(f, "{}", str::from_utf8_unchecked(mem_bio.get_buf()))

        }

    }

}