python: improve library determinism

1) Make the core python libraries deterministic.
2) Make the python libraries created by glib deterministic.

@vcunat put back the removal of share/gtk-doc in glib.

pkgs/development/interpreters/python/2.7/default.nix

@@ -72,6 +72,7 @@ let
       '';
 
     NIX_CFLAGS_COMPILE = optionalString stdenv.isDarwin "-msse2";
+    DETERMINISTIC_BUILD = 1;
 
     setupHook = ./setup-hook.sh;