[bug] Search is too inclusive

Try searching for 'stamen' here http://dotspotting.stamen.com/u/12/sheets/ Several sheets will appear that don't have 'stamen' in them: http://dotspotting.stamen.com/u/12/sheets/191/ and http://dotspotting.stamen.com/u/12/sheets/189/ (as of now, there may be more later but these are the results at 8pm on Dec 3) with 7 sheets
