Updated MD5sums and package numbers for png and zlib. Builds on Linux now.

CMake/ExternalPNG.cmake

@@ -15,8 +15,8 @@ EXTERNALPROJECT_ADD(zlib
     PREFIX ${libpng_PREFIX}
 
     DOWNLOAD_DIR ${POLYCODE_DEPS_DOWNLOAD_DIR}
-    URL http://zlib.net/zlib-1.2.5.tar.gz
-    URL_MD5 c735eab2d659a96e5a594c9e8541ad63
+    URL http://zlib.net/zlib-1.2.6.tar.gz
+    URL_MD5 618e944d7c7cd6521551e30b32322f4a
 
     PATCH_COMMAND ${CMAKE_COMMAND} -E remove <SOURCE_DIR>/zconf.h
 
@@ -31,8 +31,8 @@ EXTERNALPROJECT_ADD(libpng
     PREFIX ${libpng_PREFIX}
 
     DOWNLOAD_DIR ${POLYCODE_DEPS_DOWNLOAD_DIR}
-    URL ftp://ftp.simplesystems.org/pub/libpng/png/src/libpng-1.5.7.tar.gz
-    URL_MD5 944b56a84b65d94054cc73d7ff965de8
+    URL ftp://ftp.simplesystems.org/pub/libpng/png/src/libpng-1.5.9.tar.gz
+    URL_MD5 c740ba66cd7074ba2471b6a4ff48e1fb
 
     INSTALL_DIR ${POLYCODE_DEPS_CORE_PREFIX}
     CMAKE_ARGS ${libpng_CMAKE_ARGS} -DCMAKE_PREFIX_PATH=${install_dir} # to find zlib