mercurial: add hg-git support

Enable this feature by putting these lines into your ~/.hgrc file:

  [extensions]
  hgext.bookmarks =
  hggit =

pkgs/applications/version-management/mercurial/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, python, makeWrapper, docutils, unzip
+{ stdenv, fetchurl, python, makeWrapper, docutils, unzip, hg-git, dulwich
 , guiSupport ? false, tk ? null, curses, cacert }:
 
 let
@@ -37,7 +37,7 @@ stdenv.mkDerivation {
     ''
       for i in $(cd $out/bin && ls); do
         wrapProgram $out/bin/$i \
-          --prefix PYTHONPATH : "$(toPythonPath "$out ${curses}")" \
+          --prefix PYTHONPATH : "$(toPythonPath "$out ${curses}"):$(toPythonPath "$out ${hg-git}"):$(toPythonPath "$out ${dulwich}")" \
           $WRAP_TK
       done
 

pkgs/top-level/all-packages.nix

@@ -11833,7 +11833,7 @@ let
   mendeley = callPackage ../applications/office/mendeley { };
 
   mercurial = callPackage ../applications/version-management/mercurial {
-    inherit (pythonPackages) curses docutils;
+    inherit (pythonPackages) curses docutils hg-git dulwich;
     guiSupport = false; # use mercurialFull to get hgk GUI
   };