Quote date when checking for more recent contributions

And ensure correct format is used to set wmf_donor last_donation_date

Change-Id: I7f27bdd522dc0b4e44a1a434a96a93b82aa05d7d
Merge branch 'master' into deployment

f755e39 Quote date when checking for more recent contributions

Change-Id: I7264b7f173248320921870e57db319ff1386221b