Custom image resizing

mindtct appears to completely ignore the pixels-per-mm input parameter
(ippmm). When processing AES4000 images, the binarized image is
completely mangled and a lot of ridge information is lost.

Resizing the AES4000's small images results in a huge imaging performance
gain.

We use imagemagick for the resizing, as it's resizing code resamples the
image too (smoothing it out), which further improves performance.

libfprint/drivers/aes4000.c

@@ -218,6 +218,7 @@ struct fp_img_driver aes4000_driver = {
 	.flags = 0,
 	.img_height = 96,
 	.img_width = 96,
+	.enlarge_factor = 3,
 
 	.init = dev_init,
 	.exit = dev_exit,