header file cleanup

see http://seclists.org/nmap-dev/2013/q4/168

Move some includes out of nmap.h: nmap.h gets included lots of places,
and unconditionally included math.h, ctype.h, errno.h, stdio.h,
sys/stat.h, fcntl.h, sys/types.h, and stdarg.h. This commit moves those
includes into the .cc files where they are necessary and out of nmap.h

Remove redundant include global_structures.h, included from nmap.h

Removed redundant code included from nmap.h

Removing #include nbase.h when nmap.h is included (redundant)

Remove duplicate #include lines

Add ifndef guards to a few .h files

nmap.cc

@@ -129,12 +129,10 @@
 #include "osscan2.h"
 #include "scan_engine.h"
 #include "idle_scan.h"
-#include "timing.h"
 #include "NmapOps.h"
 #include "MACLookup.h"
 #include "traceroute.h"
 #include "nmap_tty.h"
-#include "nmap_dns.h"
 #include "services.h"
 #include "protocols.h"
 #include "targets.h"
@@ -145,6 +143,10 @@
 #include "utils.h"
 #include "xml.h"
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
 #ifndef NOLUA
 #include "nse_main.h"
 #endif