Updated message formatting to be more compatible with Dart string interpolation.

lib/i18n/date_format.dart

Index: lib/i18n/date_format.dart
diff --git a/lib/i18n/date_format.dart b/lib/i18n/date_format.dart
index 447ec9c47505ae51a7215d08857cea2e60355146..4d91cd2cd20db633e420de09177a6b4b961a3769 100644
--- a/lib/i18n/date_format.dart
+++ b/lib/i18n/date_format.dart
@@ -125,8 +125,6 @@ class DateFormat {
     
   /**
    * Named constructors for each of the above values.
-   * These could probably be made shorter if we just set the format to the 
-   * constant and the parsing was lazy.
    */
   DateFormat.fullDate() : this.formatDefinition = _fullDate;
   DateFormat.longDate() : this.formatDefinition = _longDate;
@@ -140,8 +138,18 @@ class DateFormat {
   DateFormat.longDateTime() : this.formatDefinition = _longDateTime;
   DateFormat.mediumDateTime() : this.formatDefinition = _mediumDateTime;
   DateFormat.shortDateTime() : this.formatDefinition = _shortDateTime;
-  
+
+  /** 
+   * Explicit constructor given a particular format
+  **/  
   DateFormat(this.formatDefinition);
+  
+  /**
+   * Constructors for dates/times that use a default format.
+  **/
+  DateFormat.date() {formatDefinition = _fullDate;}
+  DateFormat.time() {formatDefinition = _fullTime;}
+  DateFormat.dateTime() {formatDefinition = _fullDateTime;}
 
   /**
    *