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

src/msw/cursor.cpp

@@ -236,12 +236,12 @@ wxCursor::wxCursor(const wxString& filename,
     switch ( kind )
     {
         case wxBITMAP_TYPE_CUR_RESOURCE:
-            hcursor = ::LoadCursor(wxGetInstance(), filename.fn_str());
+            hcursor = ::LoadCursor(wxGetInstance(), filename.t_str());
             break;
 
 #ifndef __WXWINCE__
         case wxBITMAP_TYPE_CUR:
-            hcursor = ::LoadCursorFromFile(filename.fn_str());
+            hcursor = ::LoadCursorFromFile(filename.t_str());
             break;
 #endif