Remove dependencies on registry packages

Because docker core cannot vendor non-master Go dependencies, we need to remove
dependencies on registry package. The definition of digest.Digest has been
changed to a string and the regular expressions have been ported from
docker-registry/common library.

We'll likely change this be dependent on the registry in the future when the
API stabilizies and use of the master branch becomes the norm.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/v2/regexp.go

@@ -0,0 +1,19 @@
+package v2
+
+import "regexp"
+
+// This file defines regular expressions for use in route definition. These
+// are also defined in the registry code base. Until they are in a common,
+// shared location, and exported, they must be repeated here.
+
+// RepositoryNameComponentRegexp restricts registtry path components names to
+// start with at least two letters or numbers, with following parts able to
+// separated by one period, dash or underscore.
+var RepositoryNameComponentRegexp = regexp.MustCompile(`[a-z0-9]+(?:[._-][a-z0-9]+)*`)
+
+// RepositoryNameRegexp builds on RepositoryNameComponentRegexp to allow 2 to
+// 5 path components, separated by a forward slash.
+var RepositoryNameRegexp = regexp.MustCompile(`(?:` + RepositoryNameComponentRegexp.String() + `/){1,4}` + RepositoryNameComponentRegexp.String())
+
+// TagNameRegexp matches valid tag names. From docker/docker:graph/tags.go.
+var TagNameRegexp = regexp.MustCompile(`[\w][\w.-]{0,127}`)