fix xml bug

CHANGELOG

@@ -1,4 +1,9 @@
 # Nmap Changelog ($Id$); -*-text-*-
+
+o Fix XML output so that the opening <os> tag is printed again.  The
+  line which prints this was somehow removed when NSE was integrated.
+  Thanks to Joshua Abraham for reporthing the problem.
+
 o Fix a small bug in traceroute progress output which neglected printing
   when it was completed.  This caused weirdness, especially when multiple
   hosts were scanned.  [Kris]

output.cc

@@ -1339,6 +1339,7 @@ void printosscanoutput(Target *currenths) {
   if (currenths->distance != -1)
 	distance = currenths->distance;
 
+  log_write(LOG_XML, "<os>");
   if (FPR->osscan_closedtcpport > 0) {
     log_write(LOG_XML, 
 	      "<portused state=\"closed\" proto=\"tcp\" portid=\"%hu\" />\n",