Lua: disable net.(poll|read|write) on Windows and document

These functions assume that sockets are file descriptors, never worked
properly on Windows. See also 3841c085.

modules/lua/libs/net.c

@@ -189,6 +189,7 @@ static int vlclua_net_recv( lua_State *L )
     return 1;
 }
 
+#ifndef _WIN32
 /*****************************************************************************
  *
  *****************************************************************************/
@@ -277,6 +278,7 @@ static int vlclua_fd_read( lua_State *L )
         lua_pushnil( L );
     return 1;
 }
+#endif
 
 /*****************************************************************************
  *
@@ -366,9 +368,11 @@ static const luaL_Reg vlclua_net_reg[] = {
     { "close", vlclua_net_close },
     { "send", vlclua_net_send },
     { "recv", vlclua_net_recv },
+#ifndef _WIN32
     { "poll", vlclua_net_poll },
     { "read", vlclua_fd_read },
     { "write", vlclua_fd_write },
+#endif
     { "stat", vlclua_stat }, /* Not really "net" */
     { "opendir", vlclua_opendir }, /* Not really "net" */
     { NULL, NULL }

share/lua/README.txt

@@ -185,10 +185,13 @@ net.send( fd, string, [length] ): Send data on fd.
 net.recv( fd, [max length] ): Receive data from fd.
 net.poll( { fd = events } ): Implement poll function.
   Returns the numbers of file descriptors with a non 0 revent. The function
-  modifies the input table to { fd = revents }. See "man poll".
+  modifies the input table to { fd = revents }. See "man poll". This function
+  is not available on Windows.
 net.POLLIN/POLLPRI/POLLOUT/POLLRDHUP/POLLERR/POLLHUP/POLLNVAL: poll event flags
-net.read( fd, [max length] ): Read data from fd.
-net.write( fd, string, [length] ): Write data to fd.
+net.read( fd, [max length] ): Read data from fd. This function is not
+  available on Windows.
+net.write( fd, string, [length] ): Write data to fd. This function is not
+  available on Windows.
 net.stat( path ): Stat a file. Returns a table with the following fields:
     .type
     .mode