message: Fix multi image TIFF
  TIFF files contain only a single header. In multi image TIFFs, the
  header should not be read for each image, only the IFD.
diff: @@ -181,7 +181,8 @@ impl<R: Read + Seek> TIFFDecoder<R> {
  }
  /// Initializes the decoder.
  - pub fn init(self) -> ImageResult<TIFFDecoder<R>> {
  + pub fn init(mut self) -> ImageResult<TIFFDecoder<R>> {
  + try!(self.read_header());
  self.next_image()
  }
  @@ -189,7 +190,6 @@ impl<R: Read + Seek> TIFFDecoder<R> {
  /// If there is no further image in the TIFF file a format error is returned.
  /// To determine whether there are more images call `TIFFDecoder::more_images` instead.
  pub fn next_image(mut self) -> ImageResult<TIFFDecoder<R>> {
  - try!(self.read_header());
  self.ifd = Some(try!(self.read_ifd()));
  self.width = try!(self.get_tag_u32(ifd::Tag::ImageWidth));
  self.height = try!(self.get_tag_u32(ifd::Tag::ImageLength));
  