after updating to stable, sorcery prompted me to update libpng.
However, because of animated png patch which doesn't apply well with new version
of libpng, the casting fails.

Here is the casting log:
Found source file /var/spool/sorcery/libpng-1.2.27beta01.tar.bz2 for spell
libpng in /var/spool/sorcery
Waiting for any  Solo casts to complete... 
Waiting for any other casts of  libpng  to complete... done.
staging disabled
Building libpng 
hash checking source file libpng-1.2.27beta01.tar.bz2...
Algorithm used: sha512
Algorithm checks out
Checking spell level WORKS_FOR_ME
Spell level is an allowed level
hash verification succeeded
Unpacking source file libpng-1.2.27beta01.tar.bz2 for spell libpng.
patching file pngread.c
Hunk #1 succeeded at 405 (offset 6 lines).
Hunk #3 succeeded at 538 (offset 6 lines).
Hunk #5 succeeded at 798 (offset 6 lines).
Hunk #7 succeeded at 1112 (offset 6 lines).
patching file png.c
patching file pngget.c
patching file png.h
Hunk #1 succeeded at 956 (offset 9 lines).
Hunk #3 succeeded at 1112 (offset 9 lines).
Hunk #5 succeeded at 1809 (offset 12 lines).
Hunk #7 succeeded at 2511 (offset 12 lines).
Hunk #9 succeeded at 3012 (offset 12 lines).
Hunk #11 succeeded at 3315 (offset 12 lines).
Hunk #13 succeeded at 3606 (offset 12 lines).
patching file pngtrans.c
patching file pngconf.h
patching file pngwrite.c
Hunk #1 succeeded at 263 (offset 2 lines).
Hunk #3 succeeded at 1537 (offset 16 lines).
patching file pngset.c
Hunk #2 succeeded at 1029 (offset 15 lines).
patching file pngpread.c
Hunk #3 succeeded at 399 (offset 2 lines).
Hunk #5 succeeded at 796 (offset 2 lines).
Hunk #7 succeeded at 1774 (offset 15 lines).
patching file pngrutil.c
Hunk #2 succeeded at 2174 (offset -6 lines).
Hunk #3 FAILED at 3299.
Hunk #4 succeeded at 3360 (offset 30 lines).
1 out of 4 hunks FAILED -- saving rejects to file pngrutil.c.rej
patching file pngwutil.c
Hunk #1 succeeded at 498 (offset 2 lines).
Hunk #2 succeeded at 622 (offset 9 lines).
Hunk #3 succeeded at 660 (offset 2 lines).
Hunk #4 succeeded at 700 (offset 9 lines).
Hunk #5 succeeded at 1753 (offset 2 lines).
Hunk #6 succeeded at 2891 (offset 9 lines).
patching file pngrtran.c
Hunk #1 succeeded at 1293 (offset 15 lines).

Spells that encountered problems:
---------------------------------
libpng