Bump PKGREVISION for netpbm update.
Add some build fixes where necessary.
Update to 1.12.4.1

Changes from https://github.com/jgm/pandoc-types
1.12.4.1
 - relax cabal constraint for aeson
1.12.4
 - Added NFData instances for use with deepseq
1.12.3.3
 - Added Walkable instances for Citation.
   This address pandoc #1269 -- previously `walk` did not enter
   into Citation prefixes and suffixes.
Remove netpbm, used for updating graphics/netpbm.