signature change from IM 6.3.7 to 6.3.9

[magick]

The signature change is expected. We improved the signature algorithm to compute the signature at the actual depth of the image (e.g. 8, 10, 12, 16) and be invariant across all quantum depths of ImageMagick. For a particular 8-bit image, you will now get the same signature for Q8, Q16, Q32, and Q64 of ImageMagick. In many cases the image signatures between 6.3.7 and 6.3.9 remain the same, however, in some cases they may differ.