added op_image_tag() to return image tag (refs #1116)
added op_image_tag() to return image tag (refs #1116)

tejima/testravis,upsilon/travis-test,nise-nabe/ppcon-sns,tejima/testravis,balibali/KakiageSNS,nise-nabe/ppcon-sns,balibali/KakiageSNS,isaosano/OpenPNE3,kashiwasan/symfony-advanced,C-nakajima/OpenPNE3,ShinichiU/OpenPNE3,ShinichiU/AuthFramework,upsilon/travis-test,openpne/OpenPNE3,isaosano/OpenPNE3,openpne/OpenPNE3,C-nakajima/OpenPNE3,nishizoe/OpenPNE3,ShinichiU/OpenPNE3,C-nakajima/OpenPNE3,isaosano/OpenPNE3,tejima/OP3PKG,nishizoe/OpenPNE3,openpne/OpenPNE3,ShinichiU/OpenPNE3,upsilon/OpenPNE3,ShinichiU/OpenPNE3,kashiwasan/symfony-advanced,openpne/OpenPNE3,tejima/OP3PKG,ShinichiU/AuthFramework,C-nakajima/OpenPNE3,tejima/testravis,upsilon/OpenPNE3,ShinichiU/AuthFramework,isaosano/OpenPNE3