Add lang/ghc-devel for experimenting with GHC snapshots
Remove devel/hs-Cabal
devel/hs-alex: 3.1.3 --> 3.0.5 (downgrade)
x11-toolkits/hs-GLUT: 2.5.0.2 --> 2.4.0.0 (downgrade)
x11-toolkits/hs-GLURaw: 1.4.0.0 --> 1.3.0.0 (downgrade)
devel/hs-hashable: 1.2.1.0 --> 1.1.2.5 (downgrade)
devel/hs-happy: 1.19.2 --> 1.18.10 (downgrade)
www/hs-HTTP: 4000.2.10 --> 4000.2.8 (downgrade)
net/hs-network: 2.4.2.2 --> 2.4.1.2 (downgrade)
x11-toolkits/hs-OpenGL: 2.9.1.0 --> 2.8.0.0 (downgrade)
x11-toolkits/hs-OpenGLRaw: 1.4.0.0 --> 1.3.0.0 (downgrade)
devel/hs-parallel: 3.2.0.4 --> 3.2.0.3 (downgrade)
devel/hs-primitive: 0.5.1.0 --> 0.5.0.1 (downgrade)
devel/hs-syb: 0.4.1 --> 0.4.0 (downgrade)
devel/hs-vector: 0.10.9.1 --> 0.10.0.1 (downgrade)
devel/hs-cabal-install: 1.18.0.2 --> 1.16.0.2 (downgrade)
devel/hs-haskell-platform: 2013.4.0.0 --> 2013.2.0.0 (downgrade)

Haskell Platform 2013.4.0.0 was cancelled.
devel/hs-unordered-containers: 0.2.3.3 --> 0.2.3.0 (downgrade)
textproc/hs-case-insensitive: 1.1.0.2 --> 1.0.0.1 (downgrade)
www/hs-yesod-platform: Move back to HP 2013.2.0.0