Thread-safe X11 libs?

[Greg Stark <gsstark@mit.edu>]

checking for thread-safe xlibs... no
configure: error: You need to have thread-safe xlibs to use x11amp.

eek? since when? I thought our Xlibs were thread safe.

here's the test:

AC_MSG_CHECKING(for thread-safe xlibs)
AC_CACHE_VAL(thread_safe_xlibs,
[AC_TRY_RUN([
#include <X11/Xlib.h>
int main()
{
   exit(!(XInitThreads()));
}],
thread_safe_xlibs=yes,
thread_safe_xlibs=no,
thread_safe_xlibs=no)])
AC_MSG_RESULT($thread_safe_xlibs)
if test $thread_safe_xlibs = no; then
  AC_MSG_ERROR([You need to have thread-safe xlibs to use x11amp.])
fi

Is this test just wrong? or are our libs wrong? 

greg