jack: change package and attr names to 'jack1' and 'jack2'

Currently, we have a 'jack' package with attrname 'jack1d' and a
'jackdbus' package with attrname 'jackaudio'. Make it consistent 'jack1'
and 'jack2' in both package name and attrname.

This aligns the naming with what can be found on the JACK homepage.

Q: what's the difference between jack1 and jack2?
A: http://trac.jackaudio.org/wiki/Q_differenc_jack1_jack2

pkgs/applications/audio/milkytracker/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, SDL, alsaLib, autoconf, automake, jackaudio, perl
+{ stdenv, fetchurl, SDL, alsaLib, autoconf, automake, jack2, perl
 , zlib, zziplib
 }:
 
@@ -32,7 +32,7 @@ stdenv.mkDerivation rec {
     export CPATH=${zlib}/lib
   '';
 
-  buildInputs = [ SDL alsaLib autoconf automake jackaudio perl zlib zziplib ];
+  buildInputs = [ SDL alsaLib autoconf automake jack2 perl zlib zziplib ];
 
   meta = {
     description = "Music tracker application, similar to Fasttracker II.";