Contribs: update libxml2 to 2.8.0

contrib/src/libxml2/SHA512SUMS

-cb5d88f95feffde6a805a7583306864ad9cc909e958a1044afc6d5864ec480da545343f25c10bba99be59c2344e98d4cd2dcc8a152407a0ce581a51ce214d6bc  libxml2-2.7.8.tar.gz
+e36ca96e5ba18f767346f1310c43d3c8c9a35c53252de18ad63ebce7f1f8df7ae40dd0719b2c6d78f5a64e61be154eec63a36ae738d29e93a9139c524a289ad4  libxml2-2.8.0.tar.gz

contrib/src/libxml2/pthread.patch

---- libxml2/configure.in.orig	2012-05-29 12:43:39.843757694 -0400
-+++ libxml2/configure.in	2012-05-29 12:47:39.347755607 -0400
-@@ -913,12 +913,17 @@
-     echo Enabling multithreaded support
-     dnl Use pthread by default
+--- libxml2-2.8.0/configure.in.orig	2012-05-23 10:33:55.000000000 +0200
++++ libxml2-2.8.0/configure.in	2012-08-08 00:20:20.544880094 +0200
+@@ -958,12 +958,17 @@
+     dnl Use pthread by default in other cases
+     if test -z "$THREADS_W32"; then
          if test "$with_threads" = "pthread" || test "$with_threads" = "" || test "$with_threads" = "yes" ; then
 +            LIBS_saved="$LIBS"
              AC_CHECK_HEADER(pthread.h,
@@ -18,5 +18,5 @@
                  WITH_THREADS="1"]))
 +            LIBS="$LIBS_saved"
          fi
-     case $host_os in
-        *mingw32*) if test "$THREAD_LIBS" != "-lpthread"; then
+     fi
+ 

contrib/src/libxml2/rules.mak

 # libxml2
 
-LIBXML2_VERSION := 2.7.8
+LIBXML2_VERSION := 2.8.0
 LIBXML2_URL := http://xmlsoft.org/sources/libxml2-$(LIBXML2_VERSION).tar.gz
 
 PKGS += libxml2