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/filefn.h

@@ -578,7 +578,8 @@ inline int wxLstat(const wxString& path, wxStructStat *buf)
     { return wxCRT_Lstat(path.fn_str(), buf); }
 inline int wxRmDir(const wxString& path)
     { return wxCRT_RmDir(path.fn_str()); }
-#if defined(__WINDOWS__) || (defined(__OS2__) && defined(__WATCOMC__))
+#if (defined(__WINDOWS__) && !defined(__CYGWIN__)) \
+        || (defined(__OS2__) && defined(__WATCOMC__))
 inline int wxMkDir(const wxString& path, mode_t WXUNUSED(mode) = 0)
     { return wxCRT_MkDir(path.fn_str()); }
 #else