switched to have thread support enabled by default, didn't got troubles

* configure.in: switched to have thread support enabled by default,
  didn't got troubles with ABI compatibility on Linux, hope it
  won't break on strange OSes, if yes, report the system ID
* doc/libxml2-api.xml: just rebuilt the API
Daniel
diff --git a/configure.in b/configure.in
index 68b0f7e..4bc07eb 100644
--- a/configure.in
+++ b/configure.in
@@ -364,7 +364,9 @@
 TEST_THREADS=""
 
 AC_ARG_WITH(threads, [  --with-threads          Add multithread support(off)])
-if test "$with_threads" = "yes" ; then
+if test "$with_threads" = "no" ; then
+    echo Disabling multithreaded support
+else
     echo Enabling multithreaded support
 
     AC_CHECK_HEADER(pthread.h,