thrift: make it useable with the python wrapper

The python wrapper discards derivations that lack the 'pythonPath'
attribute, so provide a (dummy) pythonPath attribute to make this work:

  pythonFull.override { extraLibs = [ thrift ]; }

pkgs/development/libraries/thrift/default.nix

@@ -15,6 +15,10 @@ stdenv.mkDerivation {
 
   enableParallelBuilding = true;
 
+  # Workaround to make the python wrapper not drop this package:
+  # pythonFull.override { extraLibs = [ thrift ]; }
+  pythonPath = [];
+
   buildInputs = [
     boost zlib libevent openssl python automake autoconf libtool pkgconfig
     bison flex