Followup r101507: don't automatically use APC for the localization cache if it is...

Followup r101507: don't automatically use APC for the localization cache if it is available. I've expressed reservations in my CR comments (issues abound wherever maintenance scripts, server farms or manualRecache are involved), but the real reason is that three people (Siebrand on CR, Antoine/hashar in person and Rusty Burchfield on bug 32602) have reported problems with the APC LC, and had to set $wgLocalisationCacheConf['store'] = 'files'; explicitly to get LC to work again.