Refactor wxGridCellDateRenderer::Parse() to make it reusable

No real changes, just create TryParseDate() helper in order to allow
reusing it from wxGridCellDateEditor too in the upcoming commit.

src/generic/gridctrl.cpp

@@ -76,6 +76,23 @@ void wxGridCellRenderer::Draw(wxGrid& grid,
 
 #if wxUSE_DATETIME
 
+bool
+wxGridPrivate::TryParseDate(wxDateTime& result,
+                            const wxString& text,
+                            const wxString& format)
+{
+    wxString::const_iterator end;
+
+    // Try parsing using the same format we use for output first.
+    if ( result.ParseFormat(text, format, &end) && end == text.end() )
+        return true;
+
+    // But fall back to free-form parsing, which notably allows us to parse
+    // strings such as "today" or "tomorrow" which would be never accepted by
+    // ParseFormat().
+    return result.ParseDate(text, &end) && end == text.end();
+}
+
 // Enables a grid cell to display a formatted date
 
 wxGridCellDateRenderer::wxGridCellDateRenderer(const wxString& outformat)
@@ -131,16 +148,7 @@ wxString wxGridCellDateRenderer::GetString(const wxGrid& grid, int row, int col)
 
 bool wxGridCellDateRenderer::Parse(const wxString& text, wxDateTime& result)
 {
-    wxString::const_iterator end;
-
-    // Try parsing using the same format we use for output first.
-    if ( result.ParseFormat(text, m_oformat, &end) && end == text.end() )
-        return true;
-
-    // But fall back to free-form parsing, which notably allows us to parse
-    // strings such as "today" or "tomorrow" which would be never accepted by
-    // ParseFormat().
-    return result.ParseDate(text, &end) && end == text.end();
+    return wxGridPrivate::TryParseDate(result, text, m_oformat);
 }
 
 void wxGridCellDateRenderer::Draw(wxGrid& grid,