update libpng to 1.5.21 and xz to 5.2.0

CHANGELOG.md

@@ -1,6 +1,6 @@
 v0.12.2 (unreleased)
 --------------------
-* use OpenSSL 1.0.1j for the Windows builds
+* external libraries updated: OpenSSL to 1.0.1j, libpng to 1.5.21 and xz to 5.2.0
 * fix build failure with unpatched Qt >= 5.3
 * **#1539**: **[qt]** using OpenType fonts now results in selectable text on Windows
 * **#1638**: **[qt]** fix incorrect rendering of JPEG images on Windows Server 2008 x64

scripts/build.py

@@ -426,8 +426,8 @@ DEPENDENT_LIBS = {
 
     'libpng': {
         'order' : 3,
-        'url' : 'http://downloads.sourceforge.net/libpng/libpng-1.5.19.tar.gz',
-        'sha1': 'c4cacb5512fab1f0b6e5673766b0d89669205756',
+        'url' : 'http://downloads.sourceforge.net/libpng/libpng-1.5.21.tar.gz',
+        'sha1': '0ce1aa25abd55ad153516a29735b8ad432b4b771',
         'build' : {
             'msvc*': {
                 'result': {
@@ -514,8 +514,8 @@ DEPENDENT_LIBS = {
 
     'xz': {
         'order' : 5,
-        'url' : 'http://tukaani.org/xz/xz-5.0.5.tar.gz',
-        'sha1': '26fec2c1e409f736e77a85e4ab314dc74987def0',
+        'url' : 'http://tukaani.org/xz/xz-5.2.0.tar.gz',
+        'sha1': 'ef6b8e0b6fd85eb1b844e555ae3ecbb3a4aa8e81',
         'build' : {
             'osx*': {
                 'result': ['bin/xz'],