Fix Cygwin 1.7 build.

Avoid using Cygwin sockets as our code assumes that we use WinSock API under
Windows currently (this might change in the future) by defining
__USE_W32_SOCKETS.

Use new, safer and more efficient cygwin_conv_path() function.

Use t_str() instead of fn_str() with Windows API taking file names, under
Cygwin they are different and using fn_str() is incorrect.

A few other minor fixes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65057 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/app.h

@@ -497,7 +497,7 @@ protected:
     wxDECLARE_NO_COPY_CLASS(wxAppConsoleBase);
 };
 
-#if defined(__UNIX__)
+#if defined(__UNIX__) && !defined(__CYGWIN__)
     #include "wx/unix/app.h"
 #else
     // this has to be a class and not a typedef as we forward declare it