quick but apparently working implementation of xi:fallback, should close

* xinclude.c: quick but apparently working implementation of
  xi:fallback, should close bug #89684
* Makefile.am test/XInclude/docs/fallback.xml
  result/XInclude/fallback.xml: added a basic test for fallback,
  and run with --nowarning to avoid a spurious warning
* configure.in: applied patch from Frederic Crozat for python
  bindings on AMD 64bits machines.
Daniel
diff --git a/configure.in b/configure.in
index 28bcada..5498602 100644
--- a/configure.in
+++ b/configure.in
@@ -230,16 +230,20 @@
 	    if test -r $prefix/include/python$PYTHON_VERSION/Python.h
 	    then
 	        PYTHON_INCLUDES='$(prefix)/include/python$(PYTHON_VERSION)'
-		PYTHON_SITE_PACKAGES='$(prefix)/lib/python$(PYTHON_VERSION)/site-packages'
+		PYTHON_SITE_PACKAGES='$(libdir)/python$(PYTHON_VERSION)/site-packages'
 	    else
 		if test -r /usr/include/python$PYTHON_VERSION/Python.h
 		then
 		    PYTHON_INCLUDES=/usr/include/python$PYTHON_VERSION
-		    PYTHON_SITE_PACKAGES='$(prefix)/lib/python$(PYTHON_VERSION)/site-packages'
+		    PYTHON_SITE_PACKAGES='$(libdir)/python$(PYTHON_VERSION)/site-packages'
 		else
 		    echo could not find python$PYTHON_VERSION/Python.h
 		fi
 	    fi
+		if ! test -d "$PYTHON_SITE_PACKAGES"
+		then
+			PYTHON_SITE_PACKAGES=`$PYTHON -c "from distutils import sysconfig; print sysconfig.get_python_lib()"`
+		fi
 	fi
     fi
 fi