moved includes to includedir/libxml2/libxml, updated the configuration

* config.h.in configure.in libxml.spec.in include/libxml/Makefile.am
  libxml-2.0.pc.in: moved includes to includedir/libxml2/libxml,
  updated the configuration scripts systems accordingly
diff --git a/configure.in b/configure.in
index a80634f..3a8eadf 100644
--- a/configure.in
+++ b/configure.in
@@ -143,7 +143,7 @@
   [AC_DEFINE(HAVE_ISINF)]))
 
 XML_LIBDIR='-L${libdir}'
-XML_INCLUDEDIR='-I${includedir}/libxml -I${includedir}'
+XML_INCLUDEDIR='-I${includedir}/libxml2/libxml -I${includedir}/libxml2'
 
 dnl
 dnl Extra flags