add functions/vendor files

vendor/github.com/docker/distribution/CHANGELOG.md

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+# Changelog
+
+## 2.5.0 (2016-06-14)
+
+### Storage
+- Ensure uploads directory is cleaned after upload is commited
+- Add ability to cap concurrent operations in filesystem driver
+- S3: Add 'us-gov-west-1' to the valid region list
+- Swift: Handle ceph not returning Last-Modified header for HEAD requests
+- Add redirect middleware
+
+#### Registry
+- Add support for blobAccessController middleware
+- Add support for layers from foreign sources
+- Remove signature store
+- Add support for Let's Encrypt
+- Correct yaml key names in configuration
+
+#### Client
+- Add option to get content digest from manifest get
+
+#### Spec
+- Update the auth spec scope grammar to reflect the fact that hostnames are optionally supported
+- Clarify API documentation around catalog fetch behavior
+
+### API
+- Support returning HTTP 429 (Too Many Requests)
+
+### Documentation
+- Update auth documentation examples to show "expires in" as int
+
+### Docker Image
+- Use Alpine Linux as base image
+
+