python/notmuch: Fix runtime dep on libnotmuch.

The Python library wants to use ctypes.CDLL() on libnotmuch, so we need
to patch in the correct store path of the shared object file.

Thanks to mog from the #nixos IRC for stumbling over this.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/top-level/python-packages.nix

@@ -9178,6 +9178,11 @@ let
 
     buildInputs = with self; [ python pkgs.notmuch ];
 
+    postPatch = ''
+      sed -i -e '/CDLL/s@"libnotmuch\.@"${pkgs.notmuch}/lib/libnotmuch.@' \
+        notmuch/globals.py
+    '';
+
     meta = {
       description = "A Python wrapper around notmuch";
       homepage = http://notmuchmail.org/;