Remove the remainder based on the optional label value.

If a facet-value is given, the autocompletion failed to calculate the remainder based on the label, since the label is what the user sees while typing.

Testcase, change:

    facetMatches : function(callback) {
      callback([
        'account', 'filter', 'access', 'title',
        { label: 'city',    category: 'location' },
        { label: 'address', category: 'location' },
        { label: 'country', category: 'location' },
        { label: 'state',   category: 'location' },
      ]);
    }

to 


    facetMatches : function(callback) {
      callback([
        'account', 'filter', 'access', 'title',
        { label: 'city',    category: 'location' },
        { label: 'address', category: 'location' },
        { label: 'country', category: 'location' },
        { label: 'state',  "value":"loc.state", category: 'location' },
      ]);
    }

and type "sta" (the state-facet should be autocompleted) and press enter.

Expected behaviour: Search query should be "loc.state:"
Result: Search query is: "text: sta loc.state:"