Fix QLocale::standaloneMonthName when d->m_data == systemData()

At the moment if d->m_data == systemData() it calls
systemLocale()->query but forgets about the standalone part
so you get the wrong data

This patch introduces the new enums so that backends can implement
properly the standaloneMonthName feature properly. At the moment the Windows
and Mac ones still return the monthName, the Unix and Blackberry ones return
the data we store in months_data.

cherry picked from qtbase/b1de018e9a1efcd0f9e298ae4c865197feb47895

Change-Id: I1054420dc696ed2be0d52bdc6567ebaf202faf12
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>