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

pkg/intl/lib/number_format.dart

Index: pkg/intl/lib/number_format.dart
diff --git a/pkg/intl/lib/number_format.dart b/pkg/intl/lib/number_format.dart
index 1745178323ca98cf0aaf510ef45f1b2f31191b4c..3f642ca173c745798ef559405fac9c705f6676b4 100644
--- a/pkg/intl/lib/number_format.dart
+++ b/pkg/intl/lib/number_format.dart
@@ -562,7 +562,7 @@ class _NumberFormatParser {
     return true;
   }
 
-  /** Variables used in [parseTrunk] and [parseTrunkCharacter]. */
+  /** Variables used in [_parseTrunk] and [parseTrunkCharacter]. */
   var decimalPos;
   var digitLeftCount;
   var zeroDigitCount;