Assume inet_pton() is missing on Windows

It's much more difficult to test for this on Windows since the
headers have version guards. Just play it safe and assume it is
missing. We can remove this check when we raise the base requirements
to Vista (or newer).

CMakeLists.txt

@@ -321,7 +321,12 @@ else()
   set(CMAKE_EXTRA_INCLUDE_FILES sys/socket.h)
 endif()
 check_function_exists(inet_aton HAVE_INET_ATON)
+# This might give a false positive on Windows as it is also guarded by
+# a version check that we do not satisfy (requires Vista, but we target
+# Windows 2000).
+if(NOT WIN32)
 check_function_exists(inet_pton HAVE_INET_PTON)
+endif()
 check_function_exists(getaddrinfo HAVE_GETADDRINFO)
 set(CMAKE_EXTRA_INCLUDE_FILES) 
 set(CMAKE_REQUIRED_LIBRARIES)