Bump mpv to 0.3.8
haskell-download-curl: jailbreak to fix build with recent versions of tagsoup
haskell-ghc-mod: wrap the newly added ghc-modi executable

Cherry-picked from <https://github.com/NixOS/nixpkgs/pull/2490>.
Merge pull request #2397 from Fuuzetsu/mpv-0.3.8

Bump mpv to 0.3.8
haskell-graphviz: jailbreak to fix build with fgl 5.x
haskell-vinyl: add version 0.3
haskell-httpd-shed: jailbreak to fix build with latest version of 'network'