gnutls: only translate winsock errors for old versions

Bugfix: https handshake fails using gnutls 3 on windows
http://sourceforge.net/tracker/index.php?func=detail&aid=3441084&group_id=976&atid=100976

New gnutls versions have an error handler that knows about Winsock
errors, which is why gnutls_transport_set_global_errno() was deprecated
and then removed.

This is a correction of commit f5bb370 (blame me) which meant to
reimplement gnutls_transport_set_global_errno(), which is not necessary.

lib/gtls.c

@@ -80,15 +80,17 @@ static void tls_log_func(int level, const char *str)
 #endif
 static bool gtls_inited = FALSE;
 
+#undef MAP_WINSOCK_ERRORS
 #if defined(GNUTLS_VERSION_NUMBER)
 #  if (GNUTLS_VERSION_NUMBER >= 0x020c00)
 #    undef gnutls_transport_set_lowat
 #    define gnutls_transport_set_lowat(A,B) Curl_nop_stmt
 #    define USE_GNUTLS_PRIORITY_SET_DIRECT 1
 #  endif
-#  if (GNUTLS_VERSION_NUMBER >= 0x020c03)
-#    undef gnutls_transport_set_global_errno
-#    define gnutls_transport_set_global_errno(A) SET_ERRNO((A))
+#  if (GNUTLS_VERSION_NUMBER < 0x020c03)
+#    ifdef USE_WINSOCK
+#      define MAP_WINSOCK_ERRORS
+#    endif
 #  endif
 #endif
 
@@ -100,6 +102,7 @@ static bool gtls_inited = FALSE;
  * us to get specific about the fourth "flags" argument, and to use arbitrary
  * private data with gnutls_transport_set_ptr if we wish.
  *
+ * For old gnutls versions, curl must translate Winsock errors:
  * When these custom push and pull callbacks fail, GNU TLS checks its own
  * session-specific error variable, and when not set also its own global
  * errno variable, in order to take appropriate action. GNU TLS does not
@@ -111,7 +114,7 @@ static bool gtls_inited = FALSE;
  * error translation must take place in these callbacks.
  */
 
-#ifdef USE_WINSOCK
+#ifdef MAP_WINSOCK_ERRORS
 #  define gtls_EINTR  4
 #  define gtls_EIO    5
 #  define gtls_EAGAIN 11
@@ -132,7 +135,7 @@ static int gtls_mapped_sockerrno(void)
 static ssize_t Curl_gtls_push(void *s, const void *buf, size_t len)
 {
   ssize_t ret = swrite(GNUTLS_POINTER_TO_INT_CAST(s), buf, len);
-#ifdef USE_WINSOCK
+#ifdef MAP_WINSOCK_ERRORS
   if(ret < 0)
     gnutls_transport_set_global_errno(gtls_mapped_sockerrno());
 #endif
@@ -142,7 +145,7 @@ static ssize_t Curl_gtls_push(void *s, const void *buf, size_t len)
 static ssize_t Curl_gtls_pull(void *s, void *buf, size_t len)
 {
   ssize_t ret = sread(GNUTLS_POINTER_TO_INT_CAST(s), buf, len);
-#ifdef USE_WINSOCK
+#ifdef MAP_WINSOCK_ERRORS
   if(ret < 0)
     gnutls_transport_set_global_errno(gtls_mapped_sockerrno());
 #endif