Delay formatting of dates in messagelist until we actually need them

-- it turns out they're very expensive.

src/com/fsck/k9/activity/MessageInfoHolder.java

@@ -1,4 +1,5 @@
 package com.fsck.k9.activity;
+import com.fsck.k9.helper.MessageHelper;
 import java.util.Date;
 
 import com.fsck.k9.mail.Message;
@@ -51,4 +52,10 @@ public class MessageInfoHolder
         return uid.hashCode();
     }
 
+    public String getDate(MessageHelper messageHelper) {
+        if (date == null) {
+            date = messageHelper.formatDate(message.getSentDate());
+        }
+        return date;
+    }
 }

src/com/fsck/k9/activity/MessageList.java

@@ -2718,7 +2718,7 @@ public class MessageList
                 holder.from.setTypeface(null, message.read ? Typeface.NORMAL : Typeface.BOLD);
             }
 
-            holder.date.setText(message.date);
+            holder.date.setText(message.getDate(mMessageHelper));
             holder.subject.setCompoundDrawablesWithIntrinsicBounds(
                 message.answered ? mAnsweredIcon : null, // left
                 null, // top

src/com/fsck/k9/helper/MessageHelper.java

@@ -66,15 +66,6 @@ public class MessageHelper
 
             target.folder = folder;
 
-            if (Utility.isDateToday(date))
-            {
-                target.date = mTodayDateFormat.format(date);
-            }
-            else
-            {
-                target.date = mDateFormat.format(date);
-            }
-
             target.hasAttachments = message.getAttachmentCount() > 0;
 
             target.read = message.isSet(Flag.SEEN);
@@ -122,4 +113,14 @@ public class MessageHelper
             Log.w(K9.LOG_TAG, "Unable to load message info", me);
         }
     }
+            public String formatDate(Date date) {
+            if (Utility.isDateToday(date))
+            {
+                return mTodayDateFormat.format(date);
+            }
+            else
+            {
+                return mDateFormat.format(date);
+            }
+            } 
 }