Add GWin32InputStream and GWin32OutputStream classes

Correspond to GUnixInputStream and GUnixOutputStream. No true async
support though. But that is how the Win32 API is, for files not
explicitly opened for so-called overlapped IO.

The API to create these streams takes Win32 HANDLEs. Not file
descriptors, because file descriptors are specific to the C library
used. The user code and GLib might be using different C libraries.

Also add a test program for the new classes, and a gio-windows-2.0.pc
file.

gio/gioerror.c

@@ -206,5 +206,32 @@ g_io_error_from_errno (gint err_no)
     }
 }
 
+#ifdef G_OS_WIN32
+
+/**
+ * g_io_error_from_win32_error:
+ * @error_code: Windows error number.
+ *
+ * Converts some common error codes into GIO error codes. The
+ * fallback value G_IO_ERROR_FAILED is returned for error codes not
+ * handled.
+ *
+ * Returns: #GIOErrorEnum value for the given error number.
+ *
+ * Since: 2.26
+ **/
+GIOErrorEnum
+g_io_error_from_win32_error (gint error_code)
+{
+  switch (error_code)
+    {
+    default:
+      return G_IO_ERROR_FAILED;
+      break;
+    }
+}
+
+#endif
+
 #define __G_IO_ERROR_C__
 #include "gioaliasdef.c"