small bugs in get_calendar()

In block if ($next) that generates link to next month, the presented words for the link should be $month_abbrev[$month[zeroise($next->month, 2)]] instead of substr($month[zeroise($next->month, 2)], 0, 3).
Also, what are assigned to $thisyear and $thismonth should be gmdate('Y', current_time('timestamp')) and gmdate('m', current_time('timestamp'). The gmt_offset is not needed here since it’s already been added in the current_time('timestamp').