CRM-13735

for contribution summary display using bar chart, while receive date grouping (Frequency selection) done by 'Year' : the chart labels are integers, this was causing chart to not appear during 'Year' grouping (Frequency selection) for receive date. 

checked the function definition of <code>$xLabels->set_labels($xValues); </code> inside <code>packages/OpenFlashChart/php-ofc-library/ofc_x_axis_labels.php </code> file which states <code>  @param $labels as an array of [x_axis_label or string]</code>