Add check for XShm. Defines HAVE_XSHM

Bug #113743 r=Roland.Mainz@informatik.med.uni-giessen.de

configure.in

@@ -1578,6 +1578,17 @@ then
         $XLIBS $XEXT_LIBS)
     AC_CHECK_HEADER(X11/extensions/Xinerama.h)
 
+    dnl ========================================================
+    dnl = Check for XShm
+    dnl ========================================================
+    AC_CHECK_LIB(Xext, XShmCreateImage, _HAVE_XSHM_XEXT=1,,
+        $XLIBS $XEXT_LIBS)
+    AC_CHECK_HEADER(X11/extensions/XShm.h)
+    if test -n "$ac_cv_header_X11_extensions_XShm_h" &&
+        test -n "$_HAVE_XSHM_XEXT"; then
+        AC_DEFINE(HAVE_XSHM)
+    fi
+
     dnl ========================================================
     dnl = Check for XIE
     dnl ========================================================