Explain better than the en_US locale is always available, fix other doc glitches.

pkg/intl/lib/generate_localized.dart

Index: pkg/intl/lib/generate_localized.dart
diff --git a/pkg/intl/lib/generate_localized.dart b/pkg/intl/lib/generate_localized.dart
index 26fb3041010493938ab28fd9643868f013d72f0f..8b68910e014c84c50854765249bec12dda194144 100644
--- a/pkg/intl/lib/generate_localized.dart
+++ b/pkg/intl/lib/generate_localized.dart
@@ -106,7 +106,8 @@ void generateIndividualMessageFile(String locale,
 }
 
 /**
- * This returns the mostly constant string used in [generated] for the
+ * This returns the mostly constant string used in
+ * [generateIndividualMessageFile] for the
  * beginning of the file, parameterized by [locale].
  */
 String prologue(String locale) => """
@@ -172,7 +173,7 @@ import 'package:$intlImportPath/intl.dart';
 """;
 
 /**
- * Constant string used in [generateMainImportfile] as the end of the file.
+ * Constant string used in [generateMainImportFile] as the end of the file.
  */
 const closing = """
     default: return null;