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

docs/changes.txt

@@ -400,6 +400,14 @@ Major new features in this release
   was added.
 
 
+2.9.2:
+------
+
+MSW:
+
+- Fix Cygwin 1.7 build (David Gangola).
+
+
 2.9.1:
 ------