Merge branch 'master' into stdenv-updates

Conflict in kerberos, which was updated both in master and in
stdenv-updates. Kept the stdenv-updates version, except pulled in the
enableParallelBuilding change from master.

Signed-off-by: Shea Levy <shea@shealevy.com>

Conflicts:
	pkgs/development/libraries/kerberos/krb5.nix