PNG release 1.5.9 (CVE-2011-3026)

(cherry picked from commit 41988c32)
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

contrib/src/png/SHA512SUMS

-ac5d3e741c61486dca7a2e42516edc117c2f1afdc2cc5143c4392a0d33b15dde1c2da5231bb96da23a588722aad82665a2c15478493fc115123c4a7a071fe927  libpng-1.5.8.tar.bz2
+1b8dc51ef60e5ac1f778672aeede58d9c0a5dc91a00738cfccfe06b07e80fea149d34c7961a1268f5ce3644647fdf5396ac0be623298ead4f35410ad16f68854  libpng-1.5.9.tar.bz2

contrib/src/png/rules.mak

 # PNG
-PNG_VERSION := 1.5.8
+PNG_VERSION := 1.5.9
 PNG_URL := $(SF)/libpng/libpng-$(PNG_VERSION).tar.bz2
 
 PKGS += png