all-packages: add gitMinimal, use it for nix-exec and fetchgit

since git is used to bootstrap a lot, this can save lots of waiting
time.
hplip: fix typo in license
Merge branch 'gitMinimal' of github.com:proger/nixpkgs

since git is used to bootstrap a lot, this can save lots of waiting
time.
rlwrap: update from 0.41 to 0.42
mpd: update to 0.19.4
haskell-hayland: revert new addition

Reverts (one half of) NixOS/nixpkgs#4999, i.e. 55bb7dd1f2abf4df. The
package doesn't compile: http://hydra.cryp.to/build/249781/log/raw.
Please re-submit when the issue has been resolved.