Move registry package into handler package

The goal is to free up the distribution/registry package to include common
registry types. This moves the webapp definitions out of the way to allow for
this change in the future.

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

docs/handlers/basicauth.go

@@ -0,0 +1,11 @@
+// +build go1.4
+
+package handlers
+
+import (
+	"net/http"
+)
+
+func basicAuth(r *http.Request) (username, password string, ok bool) {
+	return r.BasicAuth()
+}