Remove "using" directives to disambiguate type_traits for vc2012.
Remove "using" directives to disambiguate type_traits for vc2012.

git-svn-id: 6df6fa3ddd728f578ea1442598151d5900a6ed44@471 630680e5-0e50-0410-840e-4b1c322b438d

mkrautz/external-protobuf,svn2github/google-protobuf,kastnerkyle/protobuf-py3,mpapierski/protobuf,kastnerkyle/protobuf-py3,mkrautz/external-protobuf,kastnerkyle/protobuf-py3,mkrautz/external-protobuf,lcy03406/protobuf,lcy03406/protobuf,beyang/protobuf,da2ce7/protobuf,mpapierski/protobuf,patrickhartling/protobuf,svn2github/protobuf-mirror,da2ce7/protobuf,beyang/protobuf,svn2github/google-protobuf,svn2github/google-protobuf,svn2github/google-protobuf,da2ce7/protobuf,lcy03406/protobuf,GreatFruitOmsk/protobuf-py3,beyang/protobuf,GreatFruitOmsk/protobuf-py3,mkrautz/external-protobuf,lcy03406/protobuf,da2ce7/protobuf,mpapierski/protobuf,Distrotech/protobuf,beyang/protobuf,beyang/protobuf,svn2github/protobuf-mirror,svn2github/protobuf-mirror,GreatFruitOmsk/protobuf-py3,Distrotech/protobuf,GreatFruitOmsk/protobuf-py3,patrickhartling/protobuf,mpapierski/protobuf,kastnerkyle/protobuf-py3,svn2github/protobuf-mirror,lcy03406/protobuf,patrickhartling/protobuf,da2ce7/protobuf,mkrautz/external-protobuf,Distrotech/protobuf,GreatFruitOmsk/protobuf-py3,patrickhartling/protobuf,svn2github/google-protobuf,patrickhartling/protobuf,svn2github/protobuf-mirror,kastnerkyle/protobuf-py3,Distrotech/protobuf,Distrotech/protobuf,mpapierski/protobuf