fix cal align for short day names

If the day names do not consist of three characters, the alignment is off
(see lcpz#522)

widget/cal.lua

@@ -53,6 +53,15 @@ local function factory(args)
         return (x + y) % 7
     end
 
+	function cal.get_dayname(day_num)
+		--- Expand day name to three chars for alignment
+		local day_name = os.date("%a", os.time { year=2006, month=1, day=day_num+cal.week_start })
+		if string.len(day_name) == 2 then
+			day_name = " "..day_name
+		end
+		return day_name
+	end
+
     function cal.build(month, year)
         local current_month, current_year = tonumber(os.date("%m")), tonumber(os.date("%Y"))
         local is_current_month = (not month or not year) or (month == current_month and year == current_year)
@@ -61,7 +70,7 @@ local function factory(args)
         local d = os.date("*t", t)
         local mth_days, st_day, this_month = d.day, (d.wday-d.day-cal.week_start+1)%7, os.date("%B %Y", t)
         local notifytable = { [1] = string.format("%s%s\n", string.rep(" ", floor((28 - this_month:len())/2)), markup.bold(this_month)) }
-        for x = 0,6 do notifytable[#notifytable+1] = os.date("%a", os.time { year=2006, month=1, day=x+cal.week_start }):sub(1, utf8.offset(1, 3)) .. " " end
+        for x = 0,6 do notifytable[#notifytable+1] = cal.get_dayname(x):sub(1, utf8.offset(1, 3)) .. " " end
         notifytable[#notifytable] = string.format("%s\n%s", notifytable[#notifytable]:sub(1, -2), string.rep(" ", st_day*4))
         local strx
         for x = 1,mth_days do