to verify winsock API availability.

using winsock or winsock2 API.

Get rid of non ANSI/ISO isascii().

  (ares_init.c/get_iphlpapi_dns_info() function): when I disable the network
  by hand or disconnect the network cable in Windows 2000 or Windows XP, my
  application gets 127.0.0.1 as the only name server. The problem comes from
  'GetNetworkParams' function, that returns the empty string "" as the only
  name server in that case. Moreover, the Windows implementation of
  inet_addr() returns INADDR_LOOPBACK instead of INADDR_NONE.

 o made ares_version.h use extern "C" for c++ compilers
 o fixed compiler warnings in ares_getnameinfo.c
 o fixed a buffer position init for TCP reads

HAVE_WINDOWS_H, HAVE_WINSOCK_H, HAVE_WINSOCK2_H, neither
HAVE_WS2TCPIP_H when __CYGWIN__ is defined.

not always zero!

Reintroduce checking for HAVE_MSG_NOSIGNAL in configure script, so that we don't depend on header inclusion order for a valid check.

Simplify check for NEED_MALLOC_H, and make more explicit that NEED_MALLOC_H shall be defined if <malloc.h> header file must be included even when including <stdlib.h>.