Factor out TempFile class and reuse it in other tests

Ensure we don't leave "mytext.dat" and "test.txt" lying around in any
directory the tests are run from by ensuring that these files are
destroyed by the test code using them.

tests/testfile.h

@@ -41,5 +41,30 @@ private:
     wxString m_name;
 };
 
+// ----------------------------------------------------------------------------
+// TempFile: just a self deleting file
+// ----------------------------------------------------------------------------
+
+class TempFile
+{
+public:
+    explicit TempFile(const wxString& name = wxString()) : m_name(name) { }
+
+    void Assign(const wxString& name) { m_name = name; }
+
+    const wxString& GetName() const { return m_name; }
+
+    ~TempFile()
+    {
+        if ( !m_name.empty() )
+            wxRemoveFile(m_name);
+    }
+
+private:
+    wxString m_name;
+
+    wxDECLARE_NO_COPY_CLASS(TempFile);
+};
+
 #endif // _WX_TESTS_TEMPFILE_H_