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

targets.h

@@ -127,29 +127,7 @@
 #ifndef TARGETS_H
 #define TARGETS_H
 
-#ifdef HAVE_CONFIG_H
-#include "nmap_config.h"
-#else
-#ifdef WIN32
-#include "nmap_winconfig.h"
-#endif /* WIN32 */
-#endif /* HAVE_CONFIG_H */
-
-/* This contains pretty much everything we need ... */
-#if HAVE_SYS_TIME_H
-#include <sys/time.h>
-#endif
-
-#if HAVE_UNISTD_H
-#include <unistd.h>
-#endif
-
-#ifdef HAVE_SYS_PARAM_H   
-#include <sys/param.h> /* Defines MAXHOSTNAMELEN on BSD*/
-#endif
-
 #include "nmap.h"
-#include "global_structures.h"
 #include "TargetGroup.h"
 
 class TargetGroup {