Contribs: udpate libxml2 to 2.9.2

Move to configure.ac

(cherry picked from commit e75e8062061bd515b3734bfd11a55e7204fd0fd6)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/libxml2/SHA512SUMS

-7b10de749485bc2eb2108063e97d89e70d6fbb78b1bf195ab5528c8c64e79483d55223a49d95934f4e00b00e906c18bdd34344703ffe158dcf08096905a44c1b  libxml2-2.9.1.tar.gz
+a4e3b20e2efceed39c20379b32b746d4a1cf65c0cf7719d26c9bf7483c1f04a4e5a442ae2f36dc4ae8a4d011b67cfb58d9f6d0be034fa3e897a49059c9289565  libxml2-2.9.2.tar.gz

contrib/src/libxml2/pthread.patch

---- 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 @@
+--- libxml2-2.9.2/configure.ac	2015-01-21 10:40:13.706152933 +0100
++++ libxml2-2.9.2/configure.ac.new	2015-01-21 10:39:36.014876563 +0100
+@@ -1049,12 +1049,17 @@
      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

contrib/src/libxml2/rules.mak

 # libxml2
 
-LIBXML2_VERSION := 2.9.1
+LIBXML2_VERSION := 2.9.2
 LIBXML2_URL := http://xmlsoft.org/sources/libxml2-$(LIBXML2_VERSION).tar.gz
 
 PKGS += libxml2

contrib/src/libxml2/win32.patch

@@ -18,9 +18,9 @@
        xmlWrapStat = xmlWrapStatUtf8;
        xmlWrapOpen = xmlWrapOpenUtf8;
  #ifdef HAVE_ZLIB_H
---- libxml2/configure.in.orig	2013-08-15 11:40:51.228070119 +0200
-+++ libxml2/configure.in	2013-08-15 11:41:01.956070564 +0200
-@@ -968,7 +968,7 @@
+--- libxml2-2.9.2/configure.ac	2014-10-16 06:06:15.000000000 +0200
++++ libxml2-2.9.2/configure.ac.new	2015-01-21 10:07:09.001484882 +0100
+@@ -1041,7 +1041,7 @@
         *mingw32*) if test "$with_threads" != "pthread" && test "$with_threads" != "no"; then
                 WITH_THREADS="1"
                 THREADS_W32="1"