fix compilation error in ubuntu14.04
fix compilation error in ubuntu14.04

treefrogframework/treefrog-framework,AmiArt/treefrog-framework,AmiArt/treefrog-framework,AmiArt/treefrog-framework,treefrogframework/treefrog-framework,treefrogframework/treefrog-framework,AmiArt/treefrog-framework,treefrogframework/treefrog-framework,treefrogframework/treefrog-framework,AmiArt/treefrog-framework