fix a bug when printing calendars, add a unit test

basis/calendar/format/format-tests.factor

@@ -1,5 +1,5 @@
 USING: calendar.format calendar kernel math tools.test
-io.streams.string accessors io math.order ;
+io.streams.string accessors io math.order sequences ;
 IN: calendar.format.tests
 
 [ 0 ] [
@@ -81,3 +81,5 @@ IN: calendar.format.tests
 ] [ "Thursday, 02-Oct-2008 23:59:59 GMT" cookie-string>timestamp ] unit-test
 
 
+[ ]
+[ { 2008 2009 } [ year. ] each ] unit-test

basis/calendar/format/format.factor

@@ -66,7 +66,7 @@ M: array month. ( pair -- )
     [ month-name write bl number>string print ]
     [ 1 zeller-congruence ]
     [ (days-in-month) day-abbreviations2 " " join print ] 2tri
-    over "   " <repetition> concat write
+    over "   " <repetition> "" concat-as write
     [
         [ 1 + day. ] keep
         1 + + 7 mod zero? [ nl ] [ bl ] if