BlenderScene: use explicit namespace instead of using namespace

Fixes (using g++ Sourcery CodeBench Lite 2014.05-29 - 4.8.3 20140320):

  .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.cpp:101:33: error: specialization of 'template<class T> void Assimp::Blender::Structure::Convert(T&, const Assimp::Blender::FileDatabase&) const' in different namespace [-fpermissive]
           const FileDatabase &db) const {
                                   ^
 In file included from .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.h:49:0,
                   from .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.cpp:47:
  .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderDNA.h:266:10: error:   from definition of 'template<class T> void Assimp::Blender::Structure::Convert(T&, const Assimp::Blender::FileDatabase&) const' [-fpermissive]
       void Convert(T &dest, const FileDatabase &db) const;
            ^
  .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.cpp:121:33: error: specialization of 'template<class T> void Assimp::Blender::Structure::Convert(T&, const Assimp::Blender::FileDatabase&) const' in different namespace [-fpermissive]
           const FileDatabase &db) const {
                                   ^
  In file included from .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.h:49:0,
                   from .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderScene.cpp:47:
  .../build/assimp-5.1.4/code/AssetLib/Blender/BlenderDNA.h:266:10: error:   from definition of 'template<class T> void Assimp::Blender::Structure::Convert(T&, const Assimp::Blender::FileDatabase&) const' [-fpermissive]
       void Convert(T &dest, const FileDatabase &db) const;
            ^

Signed-off-by: Peter Seiderer <[email protected]>

code/AssetLib/Blender/BlenderScene.cpp

@@ -49,8 +49,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "BlenderDNA.h"
 #include "BlenderSceneGen.h"
 
-using namespace Assimp;
-using namespace Assimp::Blender;
+namespace Assimp {
+namespace Blender {
 
 //--------------------------------------------------------------------------------
 template <>
@@ -885,4 +885,7 @@ void DNA::RegisterConverters() {
     converters["CollectionObject"] = DNA::FactoryPair(&Structure::Allocate<CollectionObject>, &Structure::Convert<CollectionObject>);
 }
 
+} // namespace Blender
+} //namespace Assimp
+
 #endif // ASSIMP_BUILD_NO_BLEND_IMPORTER