get_image_page (MagickGetImagePage) is especially useful
for determining the overall dimensions of a GIF, which may have
frames with different widths and heights. In such cases,
get_image_width and get_image_height report the dimensions of
the last frame only.
The test image that was meant to be rotated was generated incorrectly.
It now corresponds to the following ImageMagick command:
$ convert in -rotate 90 -orient left-bottom out
cargo test passes
