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

pkg/intl/test/date_time_format_test_core.dart

Index: pkg/intl/test/date_time_format_test_core.dart
diff --git a/pkg/intl/test/date_time_format_test_core.dart b/pkg/intl/test/date_time_format_test_core.dart
index a4fb30db6e0cd23b99416ec64271144cc482d9c9..7e007e45bd3824ff4b21225eb434e45cee7a8cf6 100644
--- a/pkg/intl/test/date_time_format_test_core.dart
+++ b/pkg/intl/test/date_time_format_test_core.dart
@@ -124,7 +124,7 @@ var icuFormatNamesToTest = const [
  * Exercise all of the formats we have explicitly defined on a particular
  * locale. [expectedResults] is a map from ICU format names to the
  * expected result of formatting [date] according to that format in
- * [locale].
+ * [localeName].
  */
 testLocale(String localeName, Map expectedResults, DateTime date) {
   var intl = new Intl(localeName);