Updated libpng packages fix two security vulnerabilities

Updated libpng12 and libpng packages fix security vulnerabilities: An integer overflow leading to a heap-based buffer overflow was found in the png_set_sPLT() and png_set_text_2() API functions of libpng. An attacker could create a specially-crafted image file and render it with an application written to explicitly call png_set_sPLT() or png_set_text_2() function, could cause libpng to crash or execute arbitrary code with the permissions of the user running such an application (CVE-2013-7353). An integer overflow leading to a heap-based buffer overflow was found in the png_set_unknown_chunks() API function of libpng. An attacker could create a specially-crafted image file and render it with an application written to explicitly call png_set_unknown_chunks() function, could cause libpng to crash or execute arbitrary code with the permissions of the user running such an application (CVE-2013-7354).