add versions and constraints for packages and samples

pkg/path/pubspec.yaml

Index: pkg/path/pubspec.yaml
diff --git a/pkg/path/pubspec.yaml b/pkg/path/pubspec.yaml
index a3661220ff617f2fb226a7904ea1c7653850f07a..0dcc61d62559982f4b6414711d82be05d426dd89 100644
--- a/pkg/path/pubspec.yaml
+++ b/pkg/path/pubspec.yaml
@@ -1,4 +1,5 @@
 name: path
+version: 0.9.0
 author: Dart Team <misc@dartlang.org>
 description: >
  A string-based path manipulation library. All of the path operations you know
@@ -7,4 +8,6 @@ description: >
 homepage: http://www.dartlang.org
 documentation: http://api.dartlang.org/docs/pkg/path
 dev_dependencies:
-  unittest: any
+  unittest: ">=0.9.0 <0.10.0"
+environment:
+  sdk: ">=1.0.0 <2.0.0"