Updated included headers to support compilation on Windows (using Visual C++)

- most of posix related functions and constants in unistd.h can be
  found in io.h in Visual C++
- introduced src/compat/msvc.h to adjust for compiler differences (and
  avoid updating code with #ifdef blocks for Windows support)
- removed some included headers that are not needed (both on Unix and
  Windows builds)

src/utils/geo_lookup.cc

@@ -13,10 +13,13 @@
  *
  */
 
+#ifndef WIN32
 #include <sys/socket.h>
-#include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#else
+#include <winsock2.h>
+#endif
 #include <string>
 
 #include <fstream>

src/utils/ip_tree.cc

@@ -15,10 +15,14 @@
 
 #include "src/utils/ip_tree.h"
 
+#ifndef WIN32
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#else
+#include <winsock2.h>
+#endif
 #include <string>
 
 #include <fstream>

src/utils/msc_tree.cc

@@ -15,9 +15,15 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#ifndef WIN32
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#else
+#include "src/compat/msvc.h"
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#endif
 
 #include "src/utils/msc_tree.h"
 

src/utils/string.cc

@@ -17,11 +17,6 @@
 #include <stdlib.h>
 #include <stddef.h>
 #include <string.h>
-#ifdef __OpenBSD__
-#include <glob.h>
-#else
-#include <wordexp.h>
-#endif
 #include <stdint.h>
 #include <inttypes.h>
 

src/utils/system.h

@@ -13,8 +13,6 @@
  *
  */
 
-#include <ctime>
-#include <iostream>
 #include <string>
 #include <list>