Gets the number of `placeholder` occurrences in `array`.

@private
@param {Array} array The array to inspect.
@param {*} placeholder The placeholder to search for.
@returns {number} Returns the placeholder count.
function countHolders(array, placeholder) {
	  var length = array.length,
	      result = 0;

	  while (length--) {
	    if (array[length] === placeholder) {
	      result++;
	    }
	  }
	  return result;
	}